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model_trainer

sleap_nn.training.model_trainer

This module is to train a sleap-nn model using Lightning.

Classes:

Name Description
ModelTrainer

Train sleap-nn model using PyTorch Lightning.

ModelTrainer

Train sleap-nn model using PyTorch Lightning.

This class is used to create dataloaders, train a sleap-nn model and save the model checkpoints/ logs with options to logging with wandb and csvlogger.

Parameters:

Name Type Description Default
config

OmegaConf dictionary which has the following: (i) data_config: data loading pre-processing configs. (ii) model_config: backbone and head configs to be passed to Model class. (iii) trainer_config: trainer configs like accelerator, optimiser params, etc.

required
train_labels

List of sio.Labels objects for training dataset.

required
val_labels

List of sio.Labels objects for validation dataset.

required
skeletons

List of sio.Skeleton objects in a single slp file.

required
lightning_model

One of the child classes of sleap_nn.training.lightning_modules.LightningModel.

required
model_type

Type of the model. One of single_instance, centered_instance, centroid, bottomup, multi_class_bottomup, multi_class_topdown.

required
backbone_type

Backbone model. One of unet, convnext and swint.

required
trainer

Instance of the lightning.Trainer initialized with loggers and callbacks.

required

Methods:

Name Description
get_model_trainer_from_config

Create a model trainer instance from config.

setup_config

Compute config parameters.

train

Train the lightning model.

Source code in sleap_nn/training/model_trainer.py
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@attrs.define
class ModelTrainer:
    """Train sleap-nn model using PyTorch Lightning.

    This class is used to create dataloaders, train a sleap-nn model and save the model checkpoints/ logs with options to logging
    with wandb and csvlogger.

    Args:
        config: OmegaConf dictionary which has the following:
                (i) data_config: data loading pre-processing configs.
                (ii) model_config: backbone and head configs to be passed to `Model` class.
                (iii) trainer_config: trainer configs like accelerator, optimiser params, etc.
        train_labels: List of `sio.Labels` objects for training dataset.
        val_labels: List of `sio.Labels` objects for validation dataset.
        skeletons: List of `sio.Skeleton` objects in a single slp file.
        lightning_model: One of the child classes of `sleap_nn.training.lightning_modules.LightningModel`.
        model_type: Type of the model. One of `single_instance`, `centered_instance`, `centroid`, `bottomup`, `multi_class_bottomup`, `multi_class_topdown`.
        backbone_type: Backbone model. One of `unet`, `convnext` and `swint`.
        trainer: Instance of the `lightning.Trainer` initialized with loggers and callbacks.
    """

    config: DictConfig
    _initial_config: Optional[DictConfig] = None
    train_labels: List[sio.Labels] = attrs.field(factory=list)
    val_labels: List[sio.Labels] = attrs.field(factory=list)
    skeletons: Optional[List[sio.Skeleton]] = None

    lightning_model: Optional[LightningModel] = None
    model_type: Optional[str] = None
    backbone_type: Optional[str] = None

    _profilers: dict = {
        "advanced": AdvancedProfiler(),
        "passthrough": PassThroughProfiler(),
        "pytorch": PyTorchProfiler(),
        "simple": SimpleProfiler(),
    }

    trainer: Optional[L.Trainer] = None

    @classmethod
    def get_model_trainer_from_config(
        cls,
        config: DictConfig,
        train_labels: Optional[List[sio.Labels]] = None,
        val_labels: Optional[List[sio.Labels]] = None,
    ):
        """Create a model trainer instance from config."""
        # Verify config structure.
        config = verify_training_cfg(config)

        model_trainer = cls(config=config)

        model_trainer.model_type = get_model_type_from_cfg(model_trainer.config)
        model_trainer.backbone_type = get_backbone_type_from_cfg(model_trainer.config)

        if model_trainer.config.trainer_config.seed is not None:
            model_trainer._set_seed()

        if train_labels is None and val_labels is None:
            # read labels from paths provided in the config
            train_labels = [
                sio.load_slp(path)
                for path in model_trainer.config.data_config.train_labels_path
            ]
            val_labels = (
                [
                    sio.load_slp(path)
                    for path in model_trainer.config.data_config.val_labels_path
                ]
                if model_trainer.config.data_config.val_labels_path is not None
                else None
            )
            model_trainer._setup_train_val_labels(
                labels=train_labels, val_labels=val_labels
            )
        else:
            model_trainer._setup_train_val_labels(
                labels=train_labels, val_labels=val_labels
            )

        model_trainer._initial_config = model_trainer.config.copy()
        # update config parameters
        model_trainer.setup_config()

        # Check if all videos exist across all labels
        all_videos_exist = all(
            video.exists(check_all=True)
            for labels in [*model_trainer.train_labels, *model_trainer.val_labels]
            for video in labels.videos
        )

        if not all_videos_exist:
            raise FileNotFoundError(
                "One or more video files do not exist or are not accessible."
            )

        return model_trainer

    def _set_seed(self):
        """Set seed for the current experiment."""
        seed = self.config.trainer_config.seed

        random.seed(seed)

        # torch
        torch.manual_seed(seed)

        # if cuda is available
        if torch.cuda.is_available():
            torch.cuda.manual_seed(seed)

        # lightning
        L.seed_everything(seed)

        # numpy
        np.random.seed(seed)

    def _get_trainer_devices(self):
        """Get trainer devices."""
        trainer_devices = (
            self.config.trainer_config.trainer_devices
            if self.config.trainer_config.trainer_devices is not None
            else "auto"
        )
        if (
            trainer_devices == "auto"
            and OmegaConf.select(
                self.config, "trainer_config.trainer_device_indices", default=None
            )
            is not None
        ):
            trainer_devices = len(
                OmegaConf.select(
                    self.config,
                    "trainer_config.trainer_device_indices",
                    default=None,
                )
            )
        elif trainer_devices == "auto":
            if torch.cuda.is_available():
                trainer_devices = torch.cuda.device_count()
            elif torch.backends.mps.is_available():
                trainer_devices = 1
            elif torch.xpu.is_available():
                trainer_devices = torch.xpu.device_count()
            else:
                trainer_devices = 1
        return trainer_devices

    def _is_training_frame(self, lf: "sio.LabeledFrame") -> bool:
        """Whether a frame carries a usable training target.

        Normally that means user instances. The centroid model can additionally
        train on frames that carry only user centroid annotations
        (``frame.centroids``) with no pose instance — the pure-centroid seeding
        case (label a body-center per animal before any keypoints exist).
        """
        if lf.has_user_instances:
            return True
        if self.model_type == "centroid":
            return any(not c.is_predicted for c in lf.centroids)
        return False

    def _count_labeled_frames(
        self, labels_list: List[sio.Labels], user_only: bool = True
    ) -> int:
        """Count labeled frames, optionally filtering to trainable frames only.

        Args:
            labels_list: List of Labels objects to count frames from.
            user_only: If True, count only frames with a training target
                (user instances, or — for the centroid model — user centroids).

        Returns:
            Total count of labeled frames.
        """
        total = 0
        for label in labels_list:
            if user_only:
                total += sum(1 for lf in label if self._is_training_frame(lf))
            else:
                total += len(label)
        return total

    def _filter_to_user_labeled(self, labels: sio.Labels) -> sio.Labels:
        """Filter a Labels object to only include trainable frames.

        Args:
            labels: Labels object to filter.

        Returns:
            New Labels object containing only frames with a training target
            (user instances, or user centroids for the centroid model).
        """
        # Filter labeled frames to only trainable ones
        user_lfs = [lf for lf in labels if self._is_training_frame(lf)]

        # Set instances to user instances only (empty for centroid-only frames)
        for lf in user_lfs:
            lf.instances = lf.user_instances

        # Create new Labels with filtered frames
        return sio.Labels(
            labeled_frames=user_lfs,
            videos=labels.videos,
            skeletons=labels.skeletons,
            tracks=labels.tracks,
            suggestions=labels.suggestions,
            provenance=labels.provenance,
        )

    def _split_centroid_labels(
        self, label: sio.Labels, val_fraction: float, seed: Optional[int]
    ):
        """Train/val split for the centroid model that keeps centroid-only frames.

        `sio.Labels.make_training_splits` returns only frames with user
        instances, so it would drop pure-centroid frames. This reimplements a
        deterministic fractional split over frames with a centroid training
        target (user instances OR user centroids).
        """
        frames = [lf for lf in label if self._is_training_frame(lf)]
        for lf in frames:
            lf.instances = lf.user_instances

        def mk(selected):
            return sio.Labels(
                labeled_frames=selected,
                videos=label.videos,
                skeletons=label.skeletons,
                tracks=label.tracks,
                suggestions=label.suggestions,
                provenance=label.provenance,
            )

        n = len(frames)
        if n <= 1:
            # Too few to hold out a val frame; use the same frame for both so
            # training still runs (mirrors small-dataset behavior elsewhere).
            return mk(list(frames)), mk(list(frames))
        rng = np.random.default_rng(seed)
        order = rng.permutation(n)
        n_val = max(1, int(round(n * val_fraction)))
        val_sel = [frames[i] for i in order[:n_val]]
        train_sel = [frames[i] for i in order[n_val:]]
        return mk(train_sel), mk(val_sel)

    def _setup_train_val_labels(
        self,
        labels: Optional[List[sio.Labels]] = None,
        val_labels: Optional[List[sio.Labels]] = None,
    ):
        """Create train and val labels objects. (Initialize `self.train_labels` and `self.val_labels`)."""
        logger.info(f"Creating train-val split...")
        total_train_lfs = 0
        total_val_lfs = 0
        self.skeletons = labels[0].skeletons

        # Check if we should count only user-labeled frames
        user_instances_only = OmegaConf.select(
            self.config, "data_config.user_instances_only", default=True
        )

        # check if all `.slp` file shave same skeleton structure (if multiple slp file paths are provided)
        # Mask-only labels (e.g. instance segmentation) may carry no skeleton.
        if self.skeletons:
            skeleton = self.skeletons[0]
            for index, train_label in enumerate(labels):
                if not train_label.skeletons:
                    continue
                skel_temp = train_label.skeletons[0]
                skeletons_equal = skeleton.matches(skel_temp)
                if not skeletons_equal:
                    message = f"The skeletons in the training labels: {index + 1} do not match the skeleton in the first training label file."
                    logger.error(message)
                    raise ValueError(message)

        # Check for same-data mode (train = val, for intentional overfitting)
        use_same = OmegaConf.select(
            self.config, "data_config.use_same_data_for_val", default=False
        )

        if use_same:
            # Same mode: use identical data for train and val (for overfitting)
            logger.info("Using same data for train and val (overfit mode)")
            self.train_labels = labels
            self.val_labels = labels
            total_train_lfs = self._count_labeled_frames(labels, user_instances_only)
            total_val_lfs = total_train_lfs
        elif val_labels is None or not len(val_labels):
            # if val labels are not provided, split from train
            val_fraction = OmegaConf.select(
                self.config, "data_config.validation_fraction", default=0.1
            )
            seed = self.config.trainer_config.seed

            # Warn if resuming from a checkpoint with a potentially different seed
            resume_ckpt = OmegaConf.select(
                self.config, "trainer_config.resume_ckpt_path", default=None
            )
            if resume_ckpt is not None:
                orig_config_path = Path(resume_ckpt).parent / "training_config.yaml"
                if orig_config_path.exists():
                    try:
                        orig_cfg = OmegaConf.load(orig_config_path.as_posix())
                        orig_seed = OmegaConf.select(
                            orig_cfg, "trainer_config.seed", default=None
                        )
                        if orig_seed != seed:
                            logger.warning(
                                f"Current seed ({seed}) differs from the original "
                                f"training seed ({orig_seed}) in {orig_config_path}. "
                                f"This will produce a different train/val split and "
                                f"may cause data leakage between train and val sets. "
                                f"Set `trainer_config.seed: {orig_seed}` to preserve "
                                f"the original split."
                            )
                    except Exception:
                        pass
                else:
                    logger.warning(
                        f"Resuming from checkpoint but could not find "
                        f"{orig_config_path} to verify the train/val split seed. "
                        f"Ensure `trainer_config.seed` matches the original "
                        f"training run to avoid data leakage."
                    )
            for label in labels:
                if self.model_type == "centroid":
                    # Centroid-aware split keeps pure-centroid frames that
                    # make_training_splits would drop (no user instances).
                    train_split, val_split = self._split_centroid_labels(
                        label, val_fraction, seed
                    )
                else:
                    train_split, val_split = label.make_training_splits(
                        n_train=1 - val_fraction, n_val=val_fraction, seed=seed
                    )
                self.train_labels.append(train_split)
                self.val_labels.append(val_split)
                total_train_lfs += len(train_split)
                total_val_lfs += len(val_split)
        else:
            self.train_labels = labels
            self.val_labels = val_labels
            total_train_lfs = self._count_labeled_frames(labels, user_instances_only)
            total_val_lfs = self._count_labeled_frames(val_labels, user_instances_only)

        logger.info(f"# Train Labeled frames: {total_train_lfs}")
        logger.info(f"# Val Labeled frames: {total_val_lfs}")

        # Single-instance models assume exactly one instance per frame; fail fast
        # with a clear error if any frame has more than one.
        if self.model_type == "single_instance":
            self._validate_single_instance_labels(self.train_labels, "train")
            self._validate_single_instance_labels(self.val_labels, "validation")

    def _validate_single_instance_labels(
        self, labels: List[sio.Labels], split_name: str
    ):
        """Ensure no frame has more than one instance for single-instance models.

        Single-instance confidence-map generation flattens the instance dimension
        (see `sleap_nn.data.confidence_maps.generate_confmaps`), so a frame with
        more than one instance would silently merge multiple animals into a single
        instance with `n_instances * n_nodes` "nodes" and corrupt training. This
        raises a clear error instead, naming the offending frame.

        Args:
            labels: List of `sio.Labels` objects to validate.
            split_name: Name of the split (e.g. "train", "validation") for the
                error message.

        Raises:
            ValueError: If any frame contains more than one (non-empty) instance.
        """
        user_instances_only = OmegaConf.select(
            self.config, "data_config.user_instances_only", default=True
        )
        for label in labels:
            for lf in label:
                if user_instances_only and lf.user_instances is not None:
                    instances = lf.user_instances
                else:
                    instances = lf.instances
                instances = [inst for inst in instances if not inst.is_empty]
                if len(instances) > 1:
                    video_idx = label.videos.index(lf.video)
                    raise ValueError(
                        f"Single-instance training requires at most one instance "
                        f"per frame, but the {split_name} frame at (video index "
                        f"{video_idx}, frame_idx {lf.frame_idx}) has "
                        f"{len(instances)} instances. Remove the extra instance(s) "
                        f"from this frame, or train a multi-instance (top-down or "
                        f"bottom-up) model instead."
                    )

    def _setup_preprocessing_config(self):
        """Setup preprocessing config."""
        # compute max_heigt, max_width, and crop_size (if not provided in the config)
        max_height = self.config.data_config.preprocessing.max_height
        max_width = self.config.data_config.preprocessing.max_width
        if self.model_type in (
            "centered_instance",
            "multi_class_topdown",
            "centered_instance_segmentation",
        ):
            crop_size = self.config.data_config.preprocessing.crop_size

        max_h, max_w = 0, 0
        max_crop_size = 0

        for train_label in self.train_labels:
            # compute max h and w from slp file if not provided
            if max_height is None or max_width is None:
                current_max_h, current_max_w = get_max_height_width(train_label)

                if current_max_h > max_h:
                    max_h = current_max_h
                if current_max_w > max_w:
                    max_w = current_max_w

            if self.model_type in (
                "centered_instance",
                "multi_class_topdown",
                "centered_instance_segmentation",
            ):
                # compute crop size if not provided in config
                if crop_size is None:
                    # Get padding from config or auto-compute from augmentation settings
                    padding = self.config.data_config.preprocessing.crop_padding
                    if padding is None:
                        # Auto-compute padding based on augmentation settings
                        aug_config = self.config.data_config.augmentation_config
                        if (
                            self.config.data_config.use_augmentations_train
                            and aug_config is not None
                            and aug_config.geometric is not None
                        ):
                            geo = aug_config.geometric
                            # Check if rotation is enabled (via rotation_p or affine_p)
                            rotation_enabled = (
                                geo.rotation_p is not None and geo.rotation_p > 0
                            ) or (
                                geo.rotation_p is None
                                and geo.scale_p is None
                                and geo.translate_p is None
                                and geo.affine_p > 0
                            )
                            # Check if scale is enabled (via scale_p or affine_p)
                            scale_enabled = (
                                geo.scale_p is not None and geo.scale_p > 0
                            ) or (
                                geo.rotation_p is None
                                and geo.scale_p is None
                                and geo.translate_p is None
                                and geo.affine_p > 0
                            )

                            if rotation_enabled or scale_enabled:
                                # First find the actual max bbox size from labels
                                bbox_size = find_max_instance_bbox_size(train_label)
                                bbox_size = max(
                                    bbox_size,
                                    self.config.data_config.preprocessing.min_crop_size
                                    or 100,
                                )
                                rotation_max = (
                                    max(
                                        abs(geo.rotation_min),
                                        abs(geo.rotation_max),
                                    )
                                    if rotation_enabled
                                    else 0.0
                                )
                                scale_max = geo.scale_max if scale_enabled else 1.0
                                padding = compute_augmentation_padding(
                                    bbox_size=bbox_size,
                                    rotation_max=rotation_max,
                                    scale_max=scale_max,
                                )
                            else:
                                padding = 0
                        else:
                            padding = 0

                    crop_sz = find_instance_crop_size(
                        labels=train_label,
                        padding=padding,
                        maximum_stride=self.config.model_config.backbone_config[
                            f"{self.backbone_type}"
                        ]["max_stride"],
                        min_crop_size=self.config.data_config.preprocessing.min_crop_size,
                    )

                    if crop_sz > max_crop_size:
                        max_crop_size = crop_sz

        # if preprocessing params were None, replace with computed params
        if max_height is None or max_width is None:
            self.config.data_config.preprocessing.max_height = max_h
            self.config.data_config.preprocessing.max_width = max_w

        if (
            self.model_type
            in (
                "centered_instance",
                "multi_class_topdown",
                "centered_instance_segmentation",
            )
            and crop_size is None
        ):
            self.config.data_config.preprocessing.crop_size = max_crop_size

    def _get_confmap_sigma(self, output_stride: int) -> float:
        """Return the active head's confmap sigma (input px), else ``output_stride``.

        Used to size the tiling overlap so a keypoint's Gaussian blob is not split
        across a seam. Segmentation / non-confmap heads have no sigma; callers only
        rely on this for confmap-based tiled models (Phase A).

        Args:
            output_stride: Head output stride, used as the fallback value.

        Returns:
            The confmap Gaussian sigma in input pixels.
        """
        head_cfg = self.config.model_config.head_configs[self.model_type]
        if head_cfg is not None:
            for head_layer in head_cfg:
                sub = head_cfg[head_layer]
                if sub is not None and "sigma" in sub and sub["sigma"] is not None:
                    return float(sub["sigma"])
        return float(output_stride)

    def _setup_tiling_config(self):
        """Auto-size tiling geometry from labels + backbone, writing back to config.

        No-op unless ``data_config.preprocessing.tiling.enabled``. Explicit
        ``tile_size`` / ``overlap`` values are preserved; only ``None`` values are
        auto-sized. Must run after :func:`check_output_strides` (so ``max_stride`` /
        ``output_stride`` are finalized). :func:`check_tiling` then validates and
        snaps the resulting geometry.
        """
        tiling = self.config.data_config.preprocessing.tiling
        if tiling is None or not tiling.enabled:
            return

        backbone_type = self.backbone_type
        backbone_cfg = self.config.model_config.backbone_config[f"{backbone_type}"]
        max_stride = int(backbone_cfg["max_stride"])
        output_stride = int(backbone_cfg["output_stride"])
        convs_per_block = int(backbone_cfg.get("convs_per_block", 2))
        kernel_size = int(backbone_cfg.get("kernel_size", 3))

        # Object extent + instance count across train labels.
        max_bbox_dim = 0.0
        n_instances = 0
        for train_label in self.train_labels:
            bbox = find_max_instance_bbox_size(train_label)
            if bbox > max_bbox_dim:
                max_bbox_dim = bbox
            n_instances += sum(len(lf.instances) for lf in train_label)

        try:
            backbone_margin = compute_backbone_context_margin(
                backbone_type, max_stride, convs_per_block, kernel_size
            )
        except ValueError:
            # Unsupported backbone under tiling; check_tiling emits the hard error.
            backbone_margin = 0

        # tile_size (preserve explicit).
        if tiling.tile_size is None:
            tile_size = compute_suggested_tile_size(
                max_bbox_dim, max_stride, output_stride, backbone_margin
            )
            self.config.data_config.preprocessing.tiling.tile_size = tile_size
            logger.info(
                f"Auto-sized tiling.tile_size={tile_size} "
                f"(max_bbox_dim={max_bbox_dim:.1f}, backbone_margin={backbone_margin})."
            )
        tile_size = int(self.config.data_config.preprocessing.tiling.tile_size)

        # overlap (preserve explicit; conservative + warn when labels sparse).
        if tiling.overlap is None:
            if n_instances < _SPARSE_LABEL_THRESHOLD:
                overlap = (
                    math.ceil(tiling.min_overlap_fraction * tile_size / output_stride)
                    * output_stride
                )
                logger.warning(
                    f"Only {n_instances} labeled instances "
                    f"(< {_SPARSE_LABEL_THRESHOLD}); the object-size estimate is "
                    f"unreliable. Using a conservative tiling.overlap={overlap} "
                    f"({tiling.min_overlap_fraction:.0%} of tile_size). Set "
                    "data_config.preprocessing.tiling.overlap explicitly to override."
                )
            else:
                sigma = self._get_confmap_sigma(output_stride)
                overlap = compute_suggested_tile_overlap(
                    tile_size,
                    max_bbox_dim,
                    sigma,
                    output_stride,
                    backbone_margin,
                    tiling.min_overlap_fraction,
                )
                logger.info(
                    f"Auto-sized tiling.overlap={overlap} "
                    f"(confmap_sigma={sigma}, backbone_margin={backbone_margin})."
                )
            self.config.data_config.preprocessing.tiling.overlap = overlap

        overlap = int(self.config.data_config.preprocessing.tiling.overlap)

        # samples_per_frame default: a conservative grid-tile count for a
        # representative (max-sized) frame, so train coverage ~= one grid pass
        # per frame. Written back into the live config before dataset creation.
        if tiling.samples_per_frame is None:
            scale = float(self.config.data_config.preprocessing.scale)
            rep_h = self.config.data_config.preprocessing.max_height
            rep_w = self.config.data_config.preprocessing.max_width
            if rep_h is None or rep_w is None:
                # Fall back to the first labeled frame's native size.
                shape = getattr(self.train_labels[0].videos[0], "shape", None)
                if shape is not None and len(shape) >= 3:
                    rep_h, rep_w = int(shape[1]), int(shape[2])
                else:
                    img = self.train_labels[0][0].image
                    rep_h, rep_w = int(img.shape[0]), int(img.shape[1])
            sized_hw = (int(rep_h * scale), int(rep_w * scale))
            n_tiles = len(
                generate_tile_grid(
                    sized_hw,
                    tile_size=tile_size,
                    overlap=overlap,
                    output_stride=output_stride,
                    max_stride=max_stride,
                    min_overlap_fraction=float(tiling.min_overlap_fraction),
                )
            )
            self.config.data_config.preprocessing.tiling.samples_per_frame = max(
                1, n_tiles
            )
            logger.info(
                "Auto-sized tiling.samples_per_frame="
                f"{max(1, n_tiles)} (grid tiles for a "
                f"{sized_hw[0]}x{sized_hw[1]} frame)."
            )

    def _setup_head_config(self):
        """Setup node, edge and class names in head config."""
        # if edges and part names aren't set in head configs, get it from labels object.
        head_config = self.config.model_config.head_configs[self.model_type]
        skeleton_node_names = list(self.skeletons[0].node_names)
        for key in head_config:
            if "part_names" in head_config[key].keys():
                if head_config[key]["part_names"] is None:
                    self.config.model_config.head_configs[self.model_type][key][
                        "part_names"
                    ] = self.skeletons[0].node_names
                elif list(head_config[key]["part_names"]) != skeleton_node_names:
                    # GT confidence-map generation always produces one channel
                    # per node in the skeleton (custom_datasets.py's
                    # generate_confmaps has no part_names/subset parameter), while
                    # the head's own output channel count is len(part_names). An
                    # explicit part_names that's shorter, longer, or reordered
                    # relative to the skeleton silently mismatches those two
                    # channel counts (a confusing tensor-shape error deep in the
                    # loss) or silently mislabels channels (if the same length
                    # but reordered). Catch it here, fail-fast, before any data
                    # loading/model construction.
                    message = (
                        f"model_config.head_configs.{self.model_type}.{key}"
                        f".part_names must exactly match the skeleton's node "
                        f"names (in order) -- partial/reordered subsets are not "
                        f"supported. Got {list(head_config[key]['part_names'])!r}, "
                        f"skeleton has {skeleton_node_names!r}. Set part_names to "
                        f"null to use the full skeleton automatically."
                    )
                    logger.error(message)
                    raise ValueError(message)

            if (
                "anchor_part" in head_config[key].keys()
                and head_config[key]["anchor_part"] is not None
                and self.model_type != "centroid"
            ):
                # `centroid`'s anchor_part deliberately falls back to None (mean
                # of visible nodes) when absent from the skeleton -- see the
                # comment at custom_datasets.py's centroid branch ("must NOT
                # crash"). Every other head type that consumes anchor_part
                # (centered_instance, multi_class_topdown,
                # centered_instance_segmentation) does `nodes.index(anchor_part)`
                # with no such guard, so a typo'd/nonexistent anchor_part
                # currently passes setup cleanly and only fails deep inside
                # dataset construction -- with an error message that
                # misleadingly blames `part_names`, not the actual offending
                # `anchor_part` field. Catch it here instead.
                if head_config[key]["anchor_part"] not in skeleton_node_names:
                    message = (
                        f"model_config.head_configs.{self.model_type}.{key}"
                        f".anchor_part {head_config[key]['anchor_part']!r} is not "
                        f"a node in the skeleton {skeleton_node_names!r}."
                    )
                    logger.error(message)
                    raise ValueError(message)

            if "edges" in head_config[key].keys():
                if head_config[key]["edges"] is None:
                    edges = [
                        (x.source.name, x.destination.name)
                        for x in self.skeletons[0].edges
                    ]
                    self.config.model_config.head_configs[self.model_type][key][
                        "edges"
                    ] = edges

            if "classes" in head_config[key].keys():
                if head_config[key]["classes"] is None:
                    tracks = []
                    for train_label in self.train_labels:
                        tracks.extend(
                            [x.name for x in train_label.tracks if x is not None]
                        )
                    classes = list(set(tracks))
                    if not len(classes):
                        message = (
                            f"No tracks found. ID models need tracks to be defined."
                        )
                        logger.error(message)
                        raise Exception(message)
                    self.config.model_config.head_configs[self.model_type][key][
                        "classes"
                    ] = classes

    def _setup_ckpt_path(self):
        """Setup checkpoint path."""
        # if run_name is None, assign a new dir name
        ckpt_dir = self.config.trainer_config.ckpt_dir
        if ckpt_dir is None or ckpt_dir == "" or ckpt_dir == "None":
            ckpt_dir = "."
            self.config.trainer_config.ckpt_dir = ckpt_dir
        run_name = self.config.trainer_config.run_name
        run_name_is_empty = run_name is None or run_name == "" or run_name == "None"

        # Validate: multi-GPU + disk cache requires explicit run_name
        if run_name_is_empty:
            is_disk_caching = (
                self.config.data_config.data_pipeline_fw
                == "torch_dataset_cache_img_disk"
            )
            num_devices = self._get_trainer_devices()

            if is_disk_caching and num_devices > 1:
                raise ValueError(
                    f"Multi-GPU training with disk caching requires an explicit `run_name`.\n\n"
                    f"Detected {num_devices} device(s) with "
                    f"`data_pipeline_fw='torch_dataset_cache_img_disk'`.\n"
                    f"Without an explicit run_name, each GPU worker generates a different "
                    f"timestamp-based directory, causing cache synchronization failures.\n\n"
                    f"Please provide a run_name using one of these methods:\n"
                    f"  - CLI: sleap-nn train config.yaml trainer_config.run_name=my_experiment\n"
                    f"  - Config file: Set `trainer_config.run_name: my_experiment`\n"
                    f"  - Python API: train(..., run_name='my_experiment')"
                )

            # Auto-generate timestamp-based run_name (safe for single GPU or non-disk-cache)
            sum_train_lfs = sum([len(train_label) for train_label in self.train_labels])
            sum_val_lfs = sum([len(val_label) for val_label in self.val_labels])
            run_name = (
                datetime.now().strftime("%y%m%d_%H%M%S")
                + f".{self.model_type}.n={sum_train_lfs + sum_val_lfs}"
            )

        # If checkpoint path already exists, add suffix to prevent overwriting
        if (Path(ckpt_dir) / run_name).exists() and (
            Path(ckpt_dir) / run_name / "best.ckpt"
        ).exists():
            logger.info(
                f"Checkpoint path already exists: {Path(ckpt_dir) / run_name}... adding suffix to prevent overwriting."
            )
            for i in count(1):
                new_run_name = f"{run_name}-{i}"
                if not (Path(ckpt_dir) / new_run_name).exists():
                    run_name = new_run_name
                    break

        self.config.trainer_config.run_name = run_name

        # set output dir for cache img
        if self.config.data_config.data_pipeline_fw == "torch_dataset_cache_img_disk":
            if self.config.data_config.cache_img_path is None:
                self.config.data_config.cache_img_path = (
                    Path(self.config.trainer_config.ckpt_dir)
                    / self.config.trainer_config.run_name
                )

    def _verify_model_input_channels(self):
        """Verify input channels in model_config based on input image and pretrained model weights."""
        # check in channels, verify with img channels / ensure_rgb/ ensure_grayscale
        if self.train_labels[0] is not None:
            img_channels = self.train_labels[0][0].image.shape[-1]
            if self.config.data_config.preprocessing.ensure_rgb:
                img_channels = 3
            if self.config.data_config.preprocessing.ensure_grayscale:
                img_channels = 1
            if (
                self.config.model_config.backbone_config[
                    f"{self.backbone_type}"
                ].in_channels
                != img_channels
            ):
                self.config.model_config.backbone_config[
                    f"{self.backbone_type}"
                ].in_channels = img_channels
                logger.info(
                    f"Updating backbone in_channels to {img_channels} based on the input image channels."
                )

        # verify input img channels with pretrained model ckpts (if any)
        if (
            self.backbone_type == "convnext" or self.backbone_type == "swint"
        ) and self.config.model_config.backbone_config[
            f"{self.backbone_type}"
        ].pre_trained_weights is not None:
            if (
                self.config.model_config.backbone_config[
                    f"{self.backbone_type}"
                ].in_channels
                != 3
            ):
                self.config.model_config.backbone_config[
                    f"{self.backbone_type}"
                ].in_channels = 3
                self.config.data_config.preprocessing.ensure_rgb = True
                self.config.data_config.preprocessing.ensure_grayscale = False
                logger.info(
                    f"Updating backbone in_channels to 3 based on the pretrained model weights."
                )

        # External pretrained (HuggingFace) backbones have 3-channel stems and
        # expect RGB (grayscale is replicated). Force in_channels=3 + ensure_rgb so
        # the data pipeline feeds 3-channel images and the pretrained stem loads.
        elif self.backbone_type == "pretrained":
            if self.config.model_config.backbone_config.pretrained.in_channels != 3:
                self.config.model_config.backbone_config.pretrained.in_channels = 3
                logger.info("Updating pretrained backbone in_channels to 3 (RGB stem).")
            self.config.data_config.preprocessing.ensure_rgb = True
            self.config.data_config.preprocessing.ensure_grayscale = False

        elif (
            self.backbone_type == "unet"
            and self.config.model_config.pretrained_backbone_weights is not None
        ):
            if self.config.model_config.pretrained_backbone_weights.endswith(".ckpt"):
                pretrained_backbone_ckpt = torch.load(
                    self.config.model_config.pretrained_backbone_weights,
                    map_location="cpu",  # this will be loaded on cpu as it's just used to get the input channels
                    weights_only=False,
                )
                input_channels = list(pretrained_backbone_ckpt["state_dict"].values())[
                    0
                ].shape[
                    -3
                ]  # get input channels from first layer
                if (
                    self.config.model_config.backbone_config.unet.in_channels
                    != input_channels
                ):
                    self.config.model_config.backbone_config.unet.in_channels = (
                        input_channels
                    )
                    logger.info(
                        f"Updating backbone in_channels to {input_channels} based on the pretrained model weights."
                    )

                    if input_channels == 1:
                        self.config.data_config.preprocessing.ensure_grayscale = True
                        self.config.data_config.preprocessing.ensure_rgb = False
                        logger.info(
                            f"Updating data preprocessing to ensure_grayscale to True based on the pretrained model weights."
                        )
                    elif input_channels == 3:
                        self.config.data_config.preprocessing.ensure_rgb = True
                        self.config.data_config.preprocessing.ensure_grayscale = False
                        logger.info(
                            f"Updating data preprocessing to ensure_rgb to True based on the pretrained model weights."
                        )

            elif self.config.model_config.pretrained_backbone_weights.endswith(".h5"):
                input_channels = get_keras_first_layer_channels(
                    self.config.model_config.pretrained_backbone_weights
                )
                if (
                    self.config.model_config.backbone_config.unet.in_channels
                    != input_channels
                ):
                    self.config.model_config.backbone_config.unet.in_channels = (
                        input_channels
                    )
                    logger.info(
                        f"Updating backbone in_channels to {input_channels} based on the pretrained model weights."
                    )

                    if input_channels == 1:
                        self.config.data_config.preprocessing.ensure_grayscale = True
                        self.config.data_config.preprocessing.ensure_rgb = False
                        logger.info(
                            f"Updating data preprocessing to ensure_grayscale to True based on the pretrained model weights."
                        )
                    elif input_channels == 3:
                        self.config.data_config.preprocessing.ensure_rgb = True
                        self.config.data_config.preprocessing.ensure_grayscale = False
                        logger.info(
                            f"Updating data preprocessing to ensure_rgb to True based on the pretrained model weights."
                        )

    def _verify_accelerator_config(self):
        """Verify the configured `trainer_accelerator` is available on this machine.

        A saved training config may have been created on a different machine (e.g.
        `trainer_accelerator: mps` from a Mac, reloaded on a Linux/CUDA box). Passing an
        unavailable accelerator straight to `lightning.Trainer` raises deep inside
        `train()`, after dataset/ckpt setup has already run. This check runs early
        (from `setup_config()`) and falls back to `"auto"` on a mismatch instead,
        letting the existing device-count resolution logic pick the right backend.
        """
        accelerator = self.config.trainer_config.trainer_accelerator

        if accelerator in ("auto", "cpu"):
            return

        if accelerator in ("gpu", "cuda"):
            available = torch.cuda.is_available()
        elif accelerator == "mps":
            available = (
                hasattr(torch.backends, "mps") and torch.backends.mps.is_available()
            )
        else:
            logger.info(
                f"Configured accelerator '{accelerator}' is not a recognized option; "
                "changing it to 'auto' (Lightning will select the best available device)."
            )
            self.config.trainer_config.trainer_accelerator = "auto"
            return

        if available:
            logger.info(
                f"Configured accelerator '{accelerator}' is available on this machine "
                "and will be used."
            )
        else:
            logger.info(
                f"Configured accelerator '{accelerator}' is not available on this "
                "machine; changing it to 'auto' (Lightning will select the best "
                "available device)."
            )
            self.config.trainer_config.trainer_accelerator = "auto"

    def setup_config(self):
        """Compute config parameters."""
        logger.info("Setting up config...")

        # Normalize empty strings to None for optional wandb fields
        if self.config.trainer_config.wandb.prv_runid == "":
            self.config.trainer_config.wandb.prv_runid = None

        # compute preprocessing parameters from the labels objects and fill in the config
        self._setup_preprocessing_config()

        # save skeleton to config
        skeleton_yaml = yaml.safe_load(SkeletonYAMLEncoder().encode(self.skeletons))
        skeleton_names = skeleton_yaml.keys()
        self.config["data_config"]["skeletons"] = []
        for skeleton_name in skeleton_names:
            skl = skeleton_yaml[skeleton_name]
            skl["name"] = skeleton_name
            self.config["data_config"]["skeletons"].append(skl)

        # setup head config - partnames, edges and class names
        self._setup_head_config()

        # set max stride for the backbone: convnext and swint
        if self.backbone_type == "convnext":
            self.config.model_config.backbone_config.convnext.max_stride = (
                self.config.model_config.backbone_config.convnext.stem_patch_stride
                * (2**3)
                * 2
            )
        elif self.backbone_type == "swint":
            self.config.model_config.backbone_config.swint.max_stride = (
                self.config.model_config.backbone_config.swint.stem_patch_stride
                * (2**3)
                * 2
            )

        # set output stride for backbone from head config and verify max stride
        self.config = check_output_strides(self.config)

        # auto-size + validate tiling geometry (no-op unless tiling.enabled)
        self._setup_tiling_config()
        self.config = check_tiling(self.config)

        # verify the configured accelerator is available on this machine
        self._verify_accelerator_config()

        # if trainer_devices is None, set it to "auto"
        if self.config.trainer_config.trainer_devices is None:
            self.config.trainer_config.trainer_devices = (
                "auto"
                if OmegaConf.select(
                    self.config, "trainer_config.trainer_device_indices", default=None
                )
                is None
                else len(
                    OmegaConf.select(
                        self.config,
                        "trainer_config.trainer_device_indices",
                        default=None,
                    )
                )
            )

        # setup checkpoint path (generates run_name if not specified)
        self._setup_ckpt_path()

        # Default wandb run name to trainer run_name if not specified
        # Note: This must come after _setup_ckpt_path() which generates run_name
        if self.config.trainer_config.wandb.name is None:
            self.config.trainer_config.wandb.name = self.config.trainer_config.run_name

        # verify input_channels in model_config based on input image and pretrained model weights
        self._verify_model_input_channels()

    def _setup_model_ckpt_dir(self):
        """Create the model ckpt folder and save ground truth labels."""
        ckpt_path = (
            Path(self.config.trainer_config.ckpt_dir)
            / self.config.trainer_config.run_name
        ).as_posix()
        logger.info(f"Setting up model ckpt dir: `{ckpt_path}`...")

        # Only rank 0 (or non-distributed) should create directories and save files
        if RANK in [0, -1]:
            if not Path(ckpt_path).exists():
                try:
                    Path(ckpt_path).mkdir(parents=True, exist_ok=True)
                except OSError as e:
                    message = f"Cannot create a new folder in {ckpt_path}.\n {e}"
                    logger.error(message)
                    raise OSError(message)
            # Check if we should filter to user-labeled frames only
            user_instances_only = OmegaConf.select(
                self.config, "data_config.user_instances_only", default=True
            )

            # Save train and val ground truth labels
            for idx, (train, val) in enumerate(zip(self.train_labels, self.val_labels)):
                # Filter to user-labeled frames if needed (for evaluation)
                if user_instances_only:
                    train_filtered = self._filter_to_user_labeled(train)
                    val_filtered = self._filter_to_user_labeled(val)
                else:
                    train_filtered = train
                    val_filtered = val

                train_filtered.save(
                    Path(ckpt_path) / f"labels_gt.train.{idx}.slp",
                    restore_original_videos=False,
                )
                val_filtered.save(
                    Path(ckpt_path) / f"labels_gt.val.{idx}.slp",
                    restore_original_videos=False,
                )

            # Save test ground truth labels if test paths are provided
            test_file_path = OmegaConf.select(
                self.config, "data_config.test_file_path", default=None
            )
            if test_file_path is not None:
                # Normalize to list of strings
                if isinstance(test_file_path, str):
                    test_paths = [test_file_path]
                else:
                    test_paths = list(test_file_path)

                for idx, test_path in enumerate(test_paths):
                    # Only save if it's a .slp file (not a video file)
                    if test_path.endswith(".slp") or test_path.endswith(".pkg.slp"):
                        try:
                            test_labels = sio.load_slp(test_path)
                            if user_instances_only:
                                test_filtered = self._filter_to_user_labeled(
                                    test_labels
                                )
                            else:
                                test_filtered = test_labels
                            test_filtered.save(
                                Path(ckpt_path) / f"labels_gt.test.{idx}.slp",
                                restore_original_videos=False,
                            )
                        except Exception as e:
                            logger.warning(
                                f"Could not save test ground truth for {test_path}: {e}"
                            )

    def _setup_viz_datasets(self):
        """Setup dataloaders."""
        data_viz_config = self.config.copy()
        data_viz_config.data_config.data_pipeline_fw = "torch_dataset"

        return get_train_val_datasets(
            train_labels=self.train_labels,
            val_labels=self.val_labels,
            config=data_viz_config,
            rank=-1,
        )

    def _setup_datasets(self):
        """Setup dataloaders."""
        base_cache_img_path = None
        if self.config.data_config.data_pipeline_fw == "torch_dataset_cache_img_memory":
            # check available memory. If insufficient memory, default to disk caching.
            # Account for DataLoader worker memory overhead
            train_num_workers = self.config.trainer_config.train_data_loader.num_workers
            val_num_workers = self.config.trainer_config.val_data_loader.num_workers
            max_num_workers = max(train_num_workers, val_num_workers)

            mem_available = check_cache_memory(
                self.train_labels,
                self.val_labels,
                memory_buffer=MEMORY_BUFFER,
                num_workers=max_num_workers,
            )
            if not mem_available:
                # Validate: multi-GPU + auto-generated run_name + fallback to disk cache
                original_run_name = self._initial_config.trainer_config.run_name
                run_name_was_auto = (
                    original_run_name is None
                    or original_run_name == ""
                    or original_run_name == "None"
                )
                if run_name_was_auto and self.trainer.num_devices > 1:
                    raise ValueError(
                        f"Memory caching failed and disk caching fallback requires an "
                        f"explicit `run_name` for multi-GPU training.\n\n"
                        f"Detected {self.trainer.num_devices} device(s) with insufficient "
                        f"memory for in-memory caching.\n"
                        f"Without an explicit run_name, each GPU worker generates a different "
                        f"timestamp-based directory, causing cache synchronization failures.\n\n"
                        f"Please provide a run_name using one of these methods:\n"
                        f"  - CLI: sleap-nn train config.yaml trainer_config.run_name=my_experiment\n"
                        f"  - Config file: Set `trainer_config.run_name: my_experiment`\n"
                        f"  - Python API: train(..., run_name='my_experiment')\n\n"
                        f"Alternatively, use `data_pipeline_fw='torch_dataset'` to disable caching."
                    )

                self.config.data_config.data_pipeline_fw = (
                    "torch_dataset_cache_img_disk"
                )
                base_cache_img_path = Path("./")
                logger.info(
                    f"Insufficient memory for in-memory caching. `jpg` files will be created for disk-caching."
                )
            self.config.data_config.cache_img_path = base_cache_img_path

        elif self.config.data_config.data_pipeline_fw == "torch_dataset_cache_img_disk":
            # Get cache img path
            base_cache_img_path = (
                Path(self.config.data_config.cache_img_path)
                if self.config.data_config.cache_img_path is not None
                else Path(self.config.trainer_config.ckpt_dir)
                / self.config.trainer_config.run_name
            )

            if self.config.data_config.cache_img_path is None:
                self.config.data_config.cache_img_path = base_cache_img_path

        return get_train_val_datasets(
            train_labels=self.train_labels,
            val_labels=self.val_labels,
            config=self.config,
            rank=self.trainer.global_rank,
        )

    def _setup_loggers_callbacks(self, viz_train_dataset, viz_val_dataset):
        """Create loggers and callbacks."""
        logger.info("Setting up callbacks and loggers...")
        loggers = []
        callbacks = []
        if self.config.trainer_config.save_ckpt:
            # checkpoint callback
            checkpoint_callback = ModelCheckpoint(
                save_top_k=self.config.trainer_config.model_ckpt.save_top_k,
                save_last=self.config.trainer_config.model_ckpt.save_last,
                dirpath=(
                    Path(self.config.trainer_config.ckpt_dir)
                    / self.config.trainer_config.run_name
                ).as_posix(),
                filename="best",
                monitor=self.config.trainer_config.model_ckpt.monitor,
                mode=self.config.trainer_config.model_ckpt.mode,
            )
            callbacks.append(checkpoint_callback)

            # csv log callback
            csv_log_keys = [
                "epoch",
                "train/loss",
                "val/loss",
                "learning_rate",
                "train/time",
                "val/time",
            ]
            # Negative-frame split metrics (train + val), only for model types
            # that support frame-level negatives and only when the feature is
            # enabled. Gating avoids empty columns in the common no-negatives case.
            use_negative_frames = OmegaConf.select(
                self.config, "data_config.use_negative_frames", default=False
            )
            if use_negative_frames and self.model_type in [
                "single_instance",
                "centroid",
                "bottomup",
                "multi_class_bottomup",
            ]:
                # Aggregate split metrics (all four supported model types).
                csv_log_keys.extend(
                    [
                        "train/n_positive",
                        "train/n_negative",
                        "train/loss_positive",
                        "train/loss_negative",
                        "train/loss_positive_unweighted",
                        "train/loss_negative_unweighted",
                        "val/n_positive",
                        "val/n_negative",
                        "val/loss_positive",
                        "val/loss_negative",
                        "val/loss_positive_unweighted",
                        "val/loss_negative_unweighted",
                    ]
                )
                # Per-head split metrics (two-head models only).
                if self.model_type == "bottomup":
                    csv_log_keys.extend(
                        [
                            "train/confmaps_loss_positive",
                            "train/confmaps_loss_negative",
                            "train/paf_loss_positive",
                            "train/paf_loss_negative",
                            "val/confmaps_loss_positive",
                            "val/confmaps_loss_negative",
                            "val/paf_loss_positive",
                            "val/paf_loss_negative",
                        ]
                    )
                elif self.model_type == "multi_class_bottomup":
                    csv_log_keys.extend(
                        [
                            "train/confmaps_loss_positive",
                            "train/confmaps_loss_negative",
                            "train/classmap_loss_positive",
                            "train/classmap_loss_negative",
                            "val/confmaps_loss_positive",
                            "val/confmaps_loss_negative",
                            "val/classmap_loss_positive",
                            "val/classmap_loss_negative",
                        ]
                    )
            # Add model-specific keys for wandb parity
            if self.model_type in [
                "single_instance",
                "centered_instance",
                "multi_class_topdown",
            ]:
                csv_log_keys.extend(
                    [f"train/confmaps/{name}" for name in self.skeletons[0].node_names]
                )
            if self.model_type == "bottomup":
                csv_log_keys.extend(
                    [
                        "train/confmaps_loss",
                        "train/paf_loss",
                        "val/confmaps_loss",
                        "val/paf_loss",
                    ]
                )
            if self.model_type == "multi_class_bottomup":
                csv_log_keys.extend(
                    [
                        "train/confmaps_loss",
                        "train/classmap_loss",
                        "train/class_accuracy",
                        "val/confmaps_loss",
                        "val/classmap_loss",
                        "val/class_accuracy",
                    ]
                )
            if self.model_type == "multi_class_topdown":
                csv_log_keys.extend(
                    [
                        "train/confmaps_loss",
                        "train/classvector_loss",
                        "train/class_accuracy",
                        "val/confmaps_loss",
                        "val/classvector_loss",
                        "val/class_accuracy",
                    ]
                )
            if self.model_type == "bottomup_segmentation":
                csv_log_keys.extend(
                    [
                        "train/fg_loss",
                        "train/center_loss",
                        "train/offset_loss",
                        "val/fg_loss",
                        "val/center_loss",
                        "val/offset_loss",
                        "val/fg_iou",
                    ]
                )
            if self.model_type == "centered_instance_segmentation":
                csv_log_keys.extend(
                    [
                        "train/fg_loss",
                        "val/fg_loss",
                        "val/fg_iou",
                    ]
                )
            if self.model_type == "semantic_segmentation":
                csv_log_keys.extend(
                    [
                        "train/fg_loss",
                        "val/fg_loss",
                        "val/fg_iou",
                    ]
                )
            # Eval-callback keys (only when trainer_config.eval.enabled, mirroring
            # the callback branching below). These are only computed every
            # eval.frequency epochs; CSVLoggerCallback NaN-resets them at the
            # start of each validation epoch so non-eval epochs show NaN instead
            # of silently repeating the last-computed eval value.
            if self.config.trainer_config.eval.enabled:
                if self.model_type == "centroid":
                    csv_log_keys.extend(
                        [
                            "eval/val/centroid_dist_avg",
                            "eval/val/centroid_dist_median",
                            "eval/val/centroid_dist_p90",
                            "eval/val/centroid_dist_p95",
                            "eval/val/centroid_dist_max",
                            "eval/val/centroid_precision",
                            "eval/val/centroid_recall",
                            "eval/val/centroid_f1",
                            "eval/val/centroid_n_tp",
                            "eval/val/centroid_n_fp",
                            "eval/val/centroid_n_fn",
                        ]
                    )
                elif self.model_type == "semantic_segmentation":
                    csv_log_keys.extend(
                        [
                            "eval/val/fg_mean_iou",
                            "eval/val/fg_mean_cldice",
                            "eval/val/fg_mean_boundary_iou",
                            "eval/val/fg_frame_recall",
                        ]
                    )
                elif self.model_type in (
                    "bottomup_segmentation",
                    "centered_instance_segmentation",
                ):
                    csv_log_keys.extend(
                        [
                            "eval/val/mask_mean_iou",
                            "eval/val/mask_mean_iou_all_gt",
                            "eval/val/mask_mean_cldice",
                            "eval/val/mask_precision",
                            "eval/val/mask_recall",
                            "eval/val/mask_f1",
                            "eval/val/mask_n_tp",
                            "eval/val/mask_n_fp",
                            "eval/val/mask_n_fn",
                        ]
                    )
                else:
                    csv_log_keys.extend(
                        [
                            "eval/val/mOKS",
                            "eval/val/oks_voc_mAP",
                            "eval/val/oks_voc_mAR",
                            "eval/val/distance/avg",
                            "eval/val/distance/p50",
                            "eval/val/distance/p95",
                            "eval/val/distance/p99",
                            "eval/val/mPCK",
                            "eval/val/PCK_5",
                            "eval/val/PCK_10",
                            "eval/val/visibility_precision",
                            "eval/val/visibility_recall",
                        ]
                    )
            csv_logger = CSVLoggerCallback(
                filepath=Path(self.config.trainer_config.ckpt_dir)
                / self.config.trainer_config.run_name
                / "training_log.csv",
                keys=csv_log_keys,
            )
            callbacks.append(csv_logger)

        if self.config.trainer_config.early_stopping.stop_training_on_plateau:
            # early stopping callback
            callbacks.append(
                EarlyStopping(
                    monitor="val/loss",
                    mode="min",
                    verbose=False,
                    min_delta=self.config.trainer_config.early_stopping.min_delta,
                    patience=self.config.trainer_config.early_stopping.patience,
                )
            )

        if self.config.trainer_config.use_wandb:
            # wandb logger
            wandb_config = self.config.trainer_config.wandb
            if wandb_config.wandb_mode == "offline":
                os.environ["WANDB_MODE"] = "offline"
            else:
                if RANK in [0, -1]:
                    wandb.login(key=self.config.trainer_config.wandb.api_key)
            wandb_logger = WandbLogger(
                entity=wandb_config.entity,
                project=wandb_config.project,
                name=wandb_config.name,
                save_dir=(
                    Path(self.config.trainer_config.ckpt_dir)
                    / self.config.trainer_config.run_name
                ).as_posix(),
                id=self.config.trainer_config.wandb.prv_runid,
                group=self.config.trainer_config.wandb.group,
            )
            loggers.append(wandb_logger)

            # Log message about wandb local logs cleanup
            should_delete_wandb_logs = wandb_config.delete_local_logs is True or (
                wandb_config.delete_local_logs is None
                and wandb_config.wandb_mode != "offline"
            )
            if should_delete_wandb_logs:
                logger.info(
                    "WandB local logs will be deleted after training completes. "
                    "To keep logs, set trainer_config.wandb.delete_local_logs=false"
                )

            # save the configs as yaml in the checkpoint dir
            # Mask API key in both configs to prevent saving to disk
            self.config.trainer_config.wandb.api_key = ""
            if self._initial_config is not None:
                self._initial_config.trainer_config.wandb.api_key = ""

        # zmq callbacks
        if self.config.trainer_config.zmq.controller_port is not None:
            controller_address = "tcp://127.0.0.1:" + str(
                self.config.trainer_config.zmq.controller_port
            )
            callbacks.append(TrainingControllerZMQ(address=controller_address))
        if self.config.trainer_config.zmq.publish_port is not None:
            publish_address = "tcp://127.0.0.1:" + str(
                self.config.trainer_config.zmq.publish_port
            )
            callbacks.append(ProgressReporterZMQ(address=publish_address))

        # viz callbacks - use unified callback for all visualization outputs
        if self.config.trainer_config.visualize_preds_during_training:
            viz_dir = (
                Path(self.config.trainer_config.ckpt_dir)
                / self.config.trainer_config.run_name
                / "viz"
            )
            if not Path(viz_dir).exists():
                if RANK in [0, -1]:
                    Path(viz_dir).mkdir(parents=True, exist_ok=True)

            # Get wandb viz config options
            log_wandb = self.config.trainer_config.use_wandb and OmegaConf.select(
                self.config, "trainer_config.wandb.save_viz_imgs_wandb", default=False
            )
            wandb_modes = []
            if log_wandb:
                if OmegaConf.select(
                    self.config, "trainer_config.wandb.viz_enabled", default=True
                ):
                    wandb_modes.append("direct")
                if OmegaConf.select(
                    self.config, "trainer_config.wandb.viz_boxes", default=False
                ):
                    wandb_modes.append("boxes")
                if OmegaConf.select(
                    self.config, "trainer_config.wandb.viz_masks", default=False
                ):
                    wandb_modes.append("masks")

            # Single unified callback handles all visualization outputs
            callbacks.append(
                UnifiedVizCallback(
                    model_trainer=self,
                    train_dataset=viz_train_dataset,
                    val_dataset=viz_val_dataset,
                    model_type=self.model_type,
                    save_local=self.config.trainer_config.save_ckpt,
                    local_save_dir=viz_dir,
                    log_wandb=log_wandb,
                    wandb_modes=wandb_modes if wandb_modes else ["direct"],
                    wandb_box_size=OmegaConf.select(
                        self.config, "trainer_config.wandb.viz_box_size", default=5.0
                    ),
                    wandb_confmap_threshold=OmegaConf.select(
                        self.config,
                        "trainer_config.wandb.viz_confmap_threshold",
                        default=0.1,
                    ),
                    log_wandb_table=OmegaConf.select(
                        self.config, "trainer_config.wandb.log_viz_table", default=False
                    ),
                    img_format=OmegaConf.select(
                        self.config,
                        "trainer_config.viz_img_format",
                        default="png",
                    ),
                )
            )

        # Add custom progress bar with better metric formatting
        if self.config.trainer_config.enable_progress_bar:
            callbacks.append(SleapProgressBar())

        # Add epoch-end evaluation callback if enabled
        if self.config.trainer_config.eval.enabled:
            if self.model_type == "centroid":
                # Use centroid-specific evaluation with distance-based metrics
                callbacks.append(
                    CentroidEvaluationCallback(
                        videos=self.val_labels[0].videos,
                        eval_frequency=self.config.trainer_config.eval.frequency,
                        match_threshold=self.config.trainer_config.eval.match_threshold,
                    )
                )
            elif self.model_type in (
                "bottomup_segmentation",
                "centered_instance_segmentation",
                "semantic_segmentation",
            ):
                # Segmentation has no keypoint predictions for OKS/PCK. Instance seg
                # (bottomup / centered-instance) recovers per-instance masks on the
                # shared preprocessed grid and reports instance-level mask-IoU mAP /
                # precision / recall (grouping-sensitive). Semantic (whole-frame
                # foreground) has no instances, so it runs the matching-free
                # foreground IoU / clDice / boundary-IoU variant. Both complement the
                # coarse val/fg_iou logged in validation_step.
                callbacks.append(
                    SegmentationEvaluationCallback(
                        eval_frequency=self.config.trainer_config.eval.frequency,
                        match_threshold=self.config.trainer_config.eval.match_threshold,
                        foreground=(self.model_type == "semantic_segmentation"),
                    )
                )
            else:
                # Use standard OKS/PCK evaluation for pose models
                callbacks.append(
                    EpochEndEvaluationCallback(
                        skeleton=self.skeletons[0],
                        videos=self.val_labels[0].videos,
                        eval_frequency=self.config.trainer_config.eval.frequency,
                        oks_stddev=self.config.trainer_config.eval.oks_stddev,
                        oks_scale=self.config.trainer_config.eval.oks_scale,
                    )
                )

        # Sync the tiling sampler + shared epoch tensor each epoch (tiling only).
        tiling = OmegaConf.select(
            self.config, "data_config.preprocessing.tiling", default=None
        )
        if tiling is not None and tiling.enabled:
            callbacks.append(TilingEpochCallback())

        return loggers, callbacks

    def _delete_cache_imgs(self):
        """Delete cache images in disk."""
        base_cache_img_path = Path(self.config.data_config.cache_img_path)
        train_cache_img_path = Path(base_cache_img_path) / "train_imgs"
        val_cache_img_path = Path(base_cache_img_path) / "val_imgs"

        if (train_cache_img_path).exists():
            logger.info(f"Deleting cache imgs from `{train_cache_img_path}`...")
            shutil.rmtree(
                (train_cache_img_path).as_posix(),
                ignore_errors=True,
            )

        if (val_cache_img_path).exists():
            logger.info(f"Deleting cache imgs from `{val_cache_img_path}`...")
            shutil.rmtree(
                (val_cache_img_path).as_posix(),
                ignore_errors=True,
            )

    def train(self):
        """Train the lightning model."""
        logger.info(f"Setting up for training...")
        start_setup_time = time.time()

        # initialize the labels object and update config.
        if not len(self.train_labels) or not len(self.val_labels):
            self._setup_train_val_labels(self.config)
            self.setup_config()

        # create the ckpt dir.
        self._setup_model_ckpt_dir()

        # create the train and val datasets for visualization.
        viz_train_dataset = None
        viz_val_dataset = None
        if self.config.trainer_config.visualize_preds_during_training:
            logger.info(f"Setting up visualization train and val datasets...")
            viz_train_dataset, viz_val_dataset = self._setup_viz_datasets()

        # setup loggers and callbacks for Trainer.
        logger.info(f"Setting up Trainer...")
        loggers, callbacks = self._setup_loggers_callbacks(
            viz_train_dataset=viz_train_dataset, viz_val_dataset=viz_val_dataset
        )
        # set up the strategy (for multi-gpu training)
        strategy = OmegaConf.select(
            self.config, "trainer_config.trainer_strategy", default="auto"
        )
        # set up profilers
        cfg_profiler = self.config.trainer_config.profiler
        profiler = None
        if cfg_profiler is not None:
            if cfg_profiler in self._profilers:
                profiler = self._profilers[cfg_profiler]
            else:
                message = f"{cfg_profiler} is not a valid option. Please choose one of {list(self._profilers.keys())}"
                logger.error(message)
                raise ValueError(message)

        devices = (
            OmegaConf.select(
                self.config, "trainer_config.trainer_device_indices", default=None
            )
            if OmegaConf.select(
                self.config, "trainer_config.trainer_device_indices", default=None
            )
            is not None
            else self.config.trainer_config.trainer_devices
        )
        logger.info(f"Trainer devices: {devices}")

        # if trainer devices is set to less than the number of available GPUs, use the least used GPUs
        if (
            torch.cuda.is_available()
            and self.config.trainer_config.trainer_accelerator != "cpu"
            and isinstance(self.config.trainer_config.trainer_devices, int)
            and self.config.trainer_config.trainer_devices < torch.cuda.device_count()
            and self.config.trainer_config.trainer_device_indices is None
        ):
            devices = [
                int(x)
                for x in np.argsort(get_gpu_memory())[::-1][
                    : self.config.trainer_config.trainer_devices
                ]
            ]
            # Sort device indices in ascending order for NCCL compatibility.
            # NCCL expects devices in consistent ascending order across ranks
            # to properly set up communication rings. Without sorting, DDP may
            # assign multiple ranks to the same GPU, causing "Duplicate GPU detected" errors.
            devices.sort()
            logger.info(f"Using GPUs with most available memory: {devices}")

        # create lightning.Trainer instance.
        self.trainer = L.Trainer(
            callbacks=callbacks,
            logger=loggers,
            enable_checkpointing=self.config.trainer_config.save_ckpt,
            devices=devices,
            max_epochs=self.config.trainer_config.max_epochs,
            accelerator=self.config.trainer_config.trainer_accelerator,
            enable_progress_bar=self.config.trainer_config.enable_progress_bar,
            strategy=strategy,
            profiler=profiler,
            log_every_n_steps=1,
        )

        self.trainer.strategy.barrier()

        # setup datasets
        train_dataset, val_dataset = self._setup_datasets()

        # Barrier after dataset creation to ensure all workers wait for disk caching
        # (rank 0 caches to disk, others must wait before reading cached files)
        self.trainer.strategy.barrier()

        # set-up steps per epoch
        train_steps_per_epoch = self.config.trainer_config.train_steps_per_epoch
        tiling = OmegaConf.select(
            self.config, "data_config.preprocessing.tiling", default=None
        )
        if train_steps_per_epoch is None:
            if (
                tiling is not None
                and tiling.enabled
                and tiling.steps_per_epoch is not None
            ):
                # TRAIN decouple: the tiling knob overrides the tile-count length.
                train_steps_per_epoch = tiling.steps_per_epoch
                logger.info(
                    f"train_steps_per_epoch not set; using tiling.steps_per_epoch={train_steps_per_epoch}"
                )
            else:
                train_steps_per_epoch = get_steps_per_epoch(
                    dataset=train_dataset,
                    batch_size=self.config.trainer_config.train_data_loader.batch_size,
                )
                logger.info(
                    f"train_steps_per_epoch not set; computed {train_steps_per_epoch} from training dataset"
                )
        else:
            logger.info(
                f"Using configured train_steps_per_epoch={train_steps_per_epoch}"
            )
        min_train_steps_per_epoch = self.config.trainer_config.min_train_steps_per_epoch
        if min_train_steps_per_epoch > train_steps_per_epoch:
            logger.info(
                f"train_steps_per_epoch={train_steps_per_epoch} is below "
                f"min_train_steps_per_epoch={min_train_steps_per_epoch}; using the minimum"
            )
            train_steps_per_epoch = min_train_steps_per_epoch
        self.config.trainer_config.train_steps_per_epoch = train_steps_per_epoch
        logger.info(f"Final train_steps_per_epoch={train_steps_per_epoch}")

        # VAL: always full-coverage (every grid tile visited once), NOT decoupled.
        val_steps_per_epoch = get_steps_per_epoch(
            dataset=val_dataset,
            batch_size=self.config.trainer_config.val_data_loader.batch_size,
        )

        logger.info(f"Training on {self.trainer.num_devices} device(s)")
        logger.info(f"Training on {self.trainer.strategy.root_device} accelerator")

        # initialize the lightning model.
        # need to initialize after Trainer is initialized (for trainer accelerator)
        logger.info(f"Setting up lightning module for {self.model_type} model...")
        self.lightning_model = LightningModel.get_lightning_model_from_config(
            config=self.config,
        )
        logger.info(f"Backbone model: {self.lightning_model.model.backbone}")
        logger.info(f"Head model: {self.lightning_model.model.head_layers}")
        total_params = sum(p.numel() for p in self.lightning_model.parameters())
        logger.info(f"Total model parameters: {total_params:,}")
        self.config.model_config.total_params = total_params

        # setup dataloaders
        # need to set up dataloaders after Trainer is initialized (for ddp). DistributedSampler depends on the rank
        logger.info(
            f"Input image shape: {train_dataset[0]['image'].shape if 'image' in train_dataset[0] else train_dataset[0]['instance_image'].shape}"
        )
        train_dataloader, val_dataloader = get_train_val_dataloaders(
            train_dataset=train_dataset,
            val_dataset=val_dataset,
            config=self.config,
            rank=self.trainer.global_rank,
            train_steps_per_epoch=self.config.trainer_config.train_steps_per_epoch,
            val_steps_per_epoch=val_steps_per_epoch,
            trainer_devices=self.trainer.num_devices,
        )

        if self.trainer.global_rank == 0:  # save config only in rank 0 process
            ckpt_path = (
                Path(self.config.trainer_config.ckpt_dir)
                / self.config.trainer_config.run_name
            ).as_posix()

            # Overwrite version with current sleap-nn version
            self._initial_config.sleap_nn_version = sleap_nn.__version__
            self.config.sleap_nn_version = sleap_nn.__version__

            OmegaConf.save(
                self._initial_config,
                (Path(ckpt_path) / "initial_config.yaml").as_posix(),
            )

            if self.config.trainer_config.use_wandb:
                if wandb.run is None:
                    wandb.init(
                        dir=(
                            Path(self.config.trainer_config.ckpt_dir)
                            / self.config.trainer_config.run_name
                        ).as_posix(),
                        project=self.config.trainer_config.wandb.project,
                        entity=self.config.trainer_config.wandb.entity,
                        name=self.config.trainer_config.wandb.name,
                        id=self.config.trainer_config.wandb.prv_runid,
                        group=self.config.trainer_config.wandb.group,
                    )

                # Define custom x-axes for wandb metrics
                # Epoch-level metrics use epoch as x-axis, step-level use default global_step
                wandb.define_metric("epoch")

                # Training metrics (train/ prefix for grouping) - all use epoch x-axis
                wandb.define_metric("train/*", step_metric="epoch")
                wandb.define_metric("train/confmaps/*", step_metric="epoch")

                # Validation metrics (val/ prefix for grouping)
                wandb.define_metric("val/*", step_metric="epoch")

                # Evaluation metrics (eval/ prefix for grouping)
                wandb.define_metric("eval/*", step_metric="epoch")

                # Visualization images (need explicit nested paths)
                wandb.define_metric("viz/*", step_metric="epoch")
                wandb.define_metric("viz/train/*", step_metric="epoch")
                wandb.define_metric("viz/val/*", step_metric="epoch")

                self.config.trainer_config.wandb.current_run_id = wandb.run.id
                wandb.config["run_name"] = self.config.trainer_config.wandb.name
                wandb.config["run_config"] = OmegaConf.to_container(
                    self.config, resolve=True
                )

            OmegaConf.save(
                self.config,
                (
                    Path(self.config.trainer_config.ckpt_dir)
                    / self.config.trainer_config.run_name
                    / "training_config.yaml"
                ).as_posix(),
            )

        self.trainer.strategy.barrier()

        # Flag to track if training was interrupted (not completed normally)
        training_interrupted = False

        try:
            logger.info(
                f"Finished trainer set up. [{time.time() - start_setup_time:.1f}s]"
            )
            logger.info(f"Starting training loop...")
            start_train_time = time.time()
            self.trainer.fit(
                self.lightning_model,
                train_dataloader,
                val_dataloader,
                ckpt_path=self.config.trainer_config.resume_ckpt_path,
            )

        except KeyboardInterrupt:
            logger.info("Stopping training...")
            training_interrupted = True

        finally:
            logger.info(
                f"Finished training loop. [{(time.time() - start_train_time) / 60:.1f} min]"
            )
            # Note: wandb.finish() is called in train.py after post-training evaluation

            # delete image disk caching
            if (
                self.config.data_config.data_pipeline_fw
                == "torch_dataset_cache_img_disk"
                and self.config.data_config.delete_cache_imgs_after_training
            ):
                if self.trainer.global_rank == 0:
                    self._delete_cache_imgs()

            # delete viz folder if requested
            if (
                self.config.trainer_config.visualize_preds_during_training
                and not self.config.trainer_config.keep_viz
            ):
                if self.trainer.global_rank == 0:
                    viz_dir = (
                        Path(self.config.trainer_config.ckpt_dir)
                        / self.config.trainer_config.run_name
                        / "viz"
                    )
                    if viz_dir.exists():
                        logger.info(f"Deleting viz folder at {viz_dir}...")
                        shutil.rmtree(viz_dir, ignore_errors=True)

            # Clean up entire run folder if training was interrupted (KeyboardInterrupt)
            if training_interrupted and self.trainer.global_rank == 0:
                run_dir = (
                    Path(self.config.trainer_config.ckpt_dir)
                    / self.config.trainer_config.run_name
                )
                if run_dir.exists():
                    logger.info(
                        f"Training canceled - cleaning up run folder at {run_dir}..."
                    )
                    shutil.rmtree(run_dir, ignore_errors=True)

get_model_trainer_from_config(config, train_labels=None, val_labels=None) classmethod

Create a model trainer instance from config.

Source code in sleap_nn/training/model_trainer.py
@classmethod
def get_model_trainer_from_config(
    cls,
    config: DictConfig,
    train_labels: Optional[List[sio.Labels]] = None,
    val_labels: Optional[List[sio.Labels]] = None,
):
    """Create a model trainer instance from config."""
    # Verify config structure.
    config = verify_training_cfg(config)

    model_trainer = cls(config=config)

    model_trainer.model_type = get_model_type_from_cfg(model_trainer.config)
    model_trainer.backbone_type = get_backbone_type_from_cfg(model_trainer.config)

    if model_trainer.config.trainer_config.seed is not None:
        model_trainer._set_seed()

    if train_labels is None and val_labels is None:
        # read labels from paths provided in the config
        train_labels = [
            sio.load_slp(path)
            for path in model_trainer.config.data_config.train_labels_path
        ]
        val_labels = (
            [
                sio.load_slp(path)
                for path in model_trainer.config.data_config.val_labels_path
            ]
            if model_trainer.config.data_config.val_labels_path is not None
            else None
        )
        model_trainer._setup_train_val_labels(
            labels=train_labels, val_labels=val_labels
        )
    else:
        model_trainer._setup_train_val_labels(
            labels=train_labels, val_labels=val_labels
        )

    model_trainer._initial_config = model_trainer.config.copy()
    # update config parameters
    model_trainer.setup_config()

    # Check if all videos exist across all labels
    all_videos_exist = all(
        video.exists(check_all=True)
        for labels in [*model_trainer.train_labels, *model_trainer.val_labels]
        for video in labels.videos
    )

    if not all_videos_exist:
        raise FileNotFoundError(
            "One or more video files do not exist or are not accessible."
        )

    return model_trainer

setup_config()

Compute config parameters.

Source code in sleap_nn/training/model_trainer.py
def setup_config(self):
    """Compute config parameters."""
    logger.info("Setting up config...")

    # Normalize empty strings to None for optional wandb fields
    if self.config.trainer_config.wandb.prv_runid == "":
        self.config.trainer_config.wandb.prv_runid = None

    # compute preprocessing parameters from the labels objects and fill in the config
    self._setup_preprocessing_config()

    # save skeleton to config
    skeleton_yaml = yaml.safe_load(SkeletonYAMLEncoder().encode(self.skeletons))
    skeleton_names = skeleton_yaml.keys()
    self.config["data_config"]["skeletons"] = []
    for skeleton_name in skeleton_names:
        skl = skeleton_yaml[skeleton_name]
        skl["name"] = skeleton_name
        self.config["data_config"]["skeletons"].append(skl)

    # setup head config - partnames, edges and class names
    self._setup_head_config()

    # set max stride for the backbone: convnext and swint
    if self.backbone_type == "convnext":
        self.config.model_config.backbone_config.convnext.max_stride = (
            self.config.model_config.backbone_config.convnext.stem_patch_stride
            * (2**3)
            * 2
        )
    elif self.backbone_type == "swint":
        self.config.model_config.backbone_config.swint.max_stride = (
            self.config.model_config.backbone_config.swint.stem_patch_stride
            * (2**3)
            * 2
        )

    # set output stride for backbone from head config and verify max stride
    self.config = check_output_strides(self.config)

    # auto-size + validate tiling geometry (no-op unless tiling.enabled)
    self._setup_tiling_config()
    self.config = check_tiling(self.config)

    # verify the configured accelerator is available on this machine
    self._verify_accelerator_config()

    # if trainer_devices is None, set it to "auto"
    if self.config.trainer_config.trainer_devices is None:
        self.config.trainer_config.trainer_devices = (
            "auto"
            if OmegaConf.select(
                self.config, "trainer_config.trainer_device_indices", default=None
            )
            is None
            else len(
                OmegaConf.select(
                    self.config,
                    "trainer_config.trainer_device_indices",
                    default=None,
                )
            )
        )

    # setup checkpoint path (generates run_name if not specified)
    self._setup_ckpt_path()

    # Default wandb run name to trainer run_name if not specified
    # Note: This must come after _setup_ckpt_path() which generates run_name
    if self.config.trainer_config.wandb.name is None:
        self.config.trainer_config.wandb.name = self.config.trainer_config.run_name

    # verify input_channels in model_config based on input image and pretrained model weights
    self._verify_model_input_channels()

train()

Train the lightning model.

Source code in sleap_nn/training/model_trainer.py
def train(self):
    """Train the lightning model."""
    logger.info(f"Setting up for training...")
    start_setup_time = time.time()

    # initialize the labels object and update config.
    if not len(self.train_labels) or not len(self.val_labels):
        self._setup_train_val_labels(self.config)
        self.setup_config()

    # create the ckpt dir.
    self._setup_model_ckpt_dir()

    # create the train and val datasets for visualization.
    viz_train_dataset = None
    viz_val_dataset = None
    if self.config.trainer_config.visualize_preds_during_training:
        logger.info(f"Setting up visualization train and val datasets...")
        viz_train_dataset, viz_val_dataset = self._setup_viz_datasets()

    # setup loggers and callbacks for Trainer.
    logger.info(f"Setting up Trainer...")
    loggers, callbacks = self._setup_loggers_callbacks(
        viz_train_dataset=viz_train_dataset, viz_val_dataset=viz_val_dataset
    )
    # set up the strategy (for multi-gpu training)
    strategy = OmegaConf.select(
        self.config, "trainer_config.trainer_strategy", default="auto"
    )
    # set up profilers
    cfg_profiler = self.config.trainer_config.profiler
    profiler = None
    if cfg_profiler is not None:
        if cfg_profiler in self._profilers:
            profiler = self._profilers[cfg_profiler]
        else:
            message = f"{cfg_profiler} is not a valid option. Please choose one of {list(self._profilers.keys())}"
            logger.error(message)
            raise ValueError(message)

    devices = (
        OmegaConf.select(
            self.config, "trainer_config.trainer_device_indices", default=None
        )
        if OmegaConf.select(
            self.config, "trainer_config.trainer_device_indices", default=None
        )
        is not None
        else self.config.trainer_config.trainer_devices
    )
    logger.info(f"Trainer devices: {devices}")

    # if trainer devices is set to less than the number of available GPUs, use the least used GPUs
    if (
        torch.cuda.is_available()
        and self.config.trainer_config.trainer_accelerator != "cpu"
        and isinstance(self.config.trainer_config.trainer_devices, int)
        and self.config.trainer_config.trainer_devices < torch.cuda.device_count()
        and self.config.trainer_config.trainer_device_indices is None
    ):
        devices = [
            int(x)
            for x in np.argsort(get_gpu_memory())[::-1][
                : self.config.trainer_config.trainer_devices
            ]
        ]
        # Sort device indices in ascending order for NCCL compatibility.
        # NCCL expects devices in consistent ascending order across ranks
        # to properly set up communication rings. Without sorting, DDP may
        # assign multiple ranks to the same GPU, causing "Duplicate GPU detected" errors.
        devices.sort()
        logger.info(f"Using GPUs with most available memory: {devices}")

    # create lightning.Trainer instance.
    self.trainer = L.Trainer(
        callbacks=callbacks,
        logger=loggers,
        enable_checkpointing=self.config.trainer_config.save_ckpt,
        devices=devices,
        max_epochs=self.config.trainer_config.max_epochs,
        accelerator=self.config.trainer_config.trainer_accelerator,
        enable_progress_bar=self.config.trainer_config.enable_progress_bar,
        strategy=strategy,
        profiler=profiler,
        log_every_n_steps=1,
    )

    self.trainer.strategy.barrier()

    # setup datasets
    train_dataset, val_dataset = self._setup_datasets()

    # Barrier after dataset creation to ensure all workers wait for disk caching
    # (rank 0 caches to disk, others must wait before reading cached files)
    self.trainer.strategy.barrier()

    # set-up steps per epoch
    train_steps_per_epoch = self.config.trainer_config.train_steps_per_epoch
    tiling = OmegaConf.select(
        self.config, "data_config.preprocessing.tiling", default=None
    )
    if train_steps_per_epoch is None:
        if (
            tiling is not None
            and tiling.enabled
            and tiling.steps_per_epoch is not None
        ):
            # TRAIN decouple: the tiling knob overrides the tile-count length.
            train_steps_per_epoch = tiling.steps_per_epoch
            logger.info(
                f"train_steps_per_epoch not set; using tiling.steps_per_epoch={train_steps_per_epoch}"
            )
        else:
            train_steps_per_epoch = get_steps_per_epoch(
                dataset=train_dataset,
                batch_size=self.config.trainer_config.train_data_loader.batch_size,
            )
            logger.info(
                f"train_steps_per_epoch not set; computed {train_steps_per_epoch} from training dataset"
            )
    else:
        logger.info(
            f"Using configured train_steps_per_epoch={train_steps_per_epoch}"
        )
    min_train_steps_per_epoch = self.config.trainer_config.min_train_steps_per_epoch
    if min_train_steps_per_epoch > train_steps_per_epoch:
        logger.info(
            f"train_steps_per_epoch={train_steps_per_epoch} is below "
            f"min_train_steps_per_epoch={min_train_steps_per_epoch}; using the minimum"
        )
        train_steps_per_epoch = min_train_steps_per_epoch
    self.config.trainer_config.train_steps_per_epoch = train_steps_per_epoch
    logger.info(f"Final train_steps_per_epoch={train_steps_per_epoch}")

    # VAL: always full-coverage (every grid tile visited once), NOT decoupled.
    val_steps_per_epoch = get_steps_per_epoch(
        dataset=val_dataset,
        batch_size=self.config.trainer_config.val_data_loader.batch_size,
    )

    logger.info(f"Training on {self.trainer.num_devices} device(s)")
    logger.info(f"Training on {self.trainer.strategy.root_device} accelerator")

    # initialize the lightning model.
    # need to initialize after Trainer is initialized (for trainer accelerator)
    logger.info(f"Setting up lightning module for {self.model_type} model...")
    self.lightning_model = LightningModel.get_lightning_model_from_config(
        config=self.config,
    )
    logger.info(f"Backbone model: {self.lightning_model.model.backbone}")
    logger.info(f"Head model: {self.lightning_model.model.head_layers}")
    total_params = sum(p.numel() for p in self.lightning_model.parameters())
    logger.info(f"Total model parameters: {total_params:,}")
    self.config.model_config.total_params = total_params

    # setup dataloaders
    # need to set up dataloaders after Trainer is initialized (for ddp). DistributedSampler depends on the rank
    logger.info(
        f"Input image shape: {train_dataset[0]['image'].shape if 'image' in train_dataset[0] else train_dataset[0]['instance_image'].shape}"
    )
    train_dataloader, val_dataloader = get_train_val_dataloaders(
        train_dataset=train_dataset,
        val_dataset=val_dataset,
        config=self.config,
        rank=self.trainer.global_rank,
        train_steps_per_epoch=self.config.trainer_config.train_steps_per_epoch,
        val_steps_per_epoch=val_steps_per_epoch,
        trainer_devices=self.trainer.num_devices,
    )

    if self.trainer.global_rank == 0:  # save config only in rank 0 process
        ckpt_path = (
            Path(self.config.trainer_config.ckpt_dir)
            / self.config.trainer_config.run_name
        ).as_posix()

        # Overwrite version with current sleap-nn version
        self._initial_config.sleap_nn_version = sleap_nn.__version__
        self.config.sleap_nn_version = sleap_nn.__version__

        OmegaConf.save(
            self._initial_config,
            (Path(ckpt_path) / "initial_config.yaml").as_posix(),
        )

        if self.config.trainer_config.use_wandb:
            if wandb.run is None:
                wandb.init(
                    dir=(
                        Path(self.config.trainer_config.ckpt_dir)
                        / self.config.trainer_config.run_name
                    ).as_posix(),
                    project=self.config.trainer_config.wandb.project,
                    entity=self.config.trainer_config.wandb.entity,
                    name=self.config.trainer_config.wandb.name,
                    id=self.config.trainer_config.wandb.prv_runid,
                    group=self.config.trainer_config.wandb.group,
                )

            # Define custom x-axes for wandb metrics
            # Epoch-level metrics use epoch as x-axis, step-level use default global_step
            wandb.define_metric("epoch")

            # Training metrics (train/ prefix for grouping) - all use epoch x-axis
            wandb.define_metric("train/*", step_metric="epoch")
            wandb.define_metric("train/confmaps/*", step_metric="epoch")

            # Validation metrics (val/ prefix for grouping)
            wandb.define_metric("val/*", step_metric="epoch")

            # Evaluation metrics (eval/ prefix for grouping)
            wandb.define_metric("eval/*", step_metric="epoch")

            # Visualization images (need explicit nested paths)
            wandb.define_metric("viz/*", step_metric="epoch")
            wandb.define_metric("viz/train/*", step_metric="epoch")
            wandb.define_metric("viz/val/*", step_metric="epoch")

            self.config.trainer_config.wandb.current_run_id = wandb.run.id
            wandb.config["run_name"] = self.config.trainer_config.wandb.name
            wandb.config["run_config"] = OmegaConf.to_container(
                self.config, resolve=True
            )

        OmegaConf.save(
            self.config,
            (
                Path(self.config.trainer_config.ckpt_dir)
                / self.config.trainer_config.run_name
                / "training_config.yaml"
            ).as_posix(),
        )

    self.trainer.strategy.barrier()

    # Flag to track if training was interrupted (not completed normally)
    training_interrupted = False

    try:
        logger.info(
            f"Finished trainer set up. [{time.time() - start_setup_time:.1f}s]"
        )
        logger.info(f"Starting training loop...")
        start_train_time = time.time()
        self.trainer.fit(
            self.lightning_model,
            train_dataloader,
            val_dataloader,
            ckpt_path=self.config.trainer_config.resume_ckpt_path,
        )

    except KeyboardInterrupt:
        logger.info("Stopping training...")
        training_interrupted = True

    finally:
        logger.info(
            f"Finished training loop. [{(time.time() - start_train_time) / 60:.1f} min]"
        )
        # Note: wandb.finish() is called in train.py after post-training evaluation

        # delete image disk caching
        if (
            self.config.data_config.data_pipeline_fw
            == "torch_dataset_cache_img_disk"
            and self.config.data_config.delete_cache_imgs_after_training
        ):
            if self.trainer.global_rank == 0:
                self._delete_cache_imgs()

        # delete viz folder if requested
        if (
            self.config.trainer_config.visualize_preds_during_training
            and not self.config.trainer_config.keep_viz
        ):
            if self.trainer.global_rank == 0:
                viz_dir = (
                    Path(self.config.trainer_config.ckpt_dir)
                    / self.config.trainer_config.run_name
                    / "viz"
                )
                if viz_dir.exists():
                    logger.info(f"Deleting viz folder at {viz_dir}...")
                    shutil.rmtree(viz_dir, ignore_errors=True)

        # Clean up entire run folder if training was interrupted (KeyboardInterrupt)
        if training_interrupted and self.trainer.global_rank == 0:
            run_dir = (
                Path(self.config.trainer_config.ckpt_dir)
                / self.config.trainer_config.run_name
            )
            if run_dir.exists():
                logger.info(
                    f"Training canceled - cleaning up run folder at {run_dir}..."
                )
                shutil.rmtree(run_dir, ignore_errors=True)