preparing for training adding some temporary debug code aswell to visualize model output

src/lerobot/policies/fastwam/configuration_fastwam.py

@@ -153,11 +153,25 @@ class FastWAMConfig(PreTrainedConfig):
         proprio_dim (int | None): Number of proprioception channels used as an
             extra text-context token. `None` disables proprio conditioning.
         action_horizon (int): Number of actions predicted by one policy call.
-        num_video_frames (int): Number of video frames used by FastWAM rollout.
+        num_video_frames (int): Raw video sampling window (in dataset frames). The
+            model actually operates on `model_video_frames` frames after subsampling
+            by `action_video_freq_ratio`.
+        action_video_freq_ratio (int): Actions are sampled at this multiple of the
+            video frame rate. Video frames are taken every `action_video_freq_ratio`-th
+            raw frame, so the model sees `(num_video_frames - 1) // ratio + 1` frames
+            spanning the same time window as `action_horizon` actions (ratio actions
+            per video frame).
         image_size (tuple[int, int]): Concatenated image size as `(height, width)`.
         context_len (int): Maximum text embedding token length.
         video_dit_config (dict[str, Any] | None): Wan video expert config.
         action_dit_config (dict[str, Any] | None): Action expert config.
+        use_gradient_checkpointing (bool): Enable activation checkpointing in both DiT
+            experts (trades compute for memory; propagated into the DiT configs).
+        freeze_video_expert (bool): Freeze the ~5B Wan video expert
+            (`model.video_expert`) so only the action expert + proprio encoder train.
+            Cuts the AdamW optimizer footprint substantially; the video expert keeps its
+            pretrained weights. (If enabled, also set `loss.lambda_video=0` to skip the
+            now-gradient-free video loss compute.)
     """
 
     n_obs_steps: int = 1
@@ -166,6 +180,7 @@ class FastWAMConfig(PreTrainedConfig):
     action_horizon: int = 32
     n_action_steps: int = 32
     num_video_frames: int = 33
+    action_video_freq_ratio: int = 4
     image_size: tuple[int, int] = (224, 448)
     context_len: int = 128
     model_id: str = WAN22_MODEL_ID
@@ -186,6 +201,8 @@ class FastWAMConfig(PreTrainedConfig):
     sigma_shift: float | None = None
     tiled: bool = False
     fp32_attention: bool = True
+    use_gradient_checkpointing: bool = False
+    freeze_video_expert: bool = False
     toggle_action_dimensions: list[int] = field(default_factory=list)
     video_scheduler: dict[str, float | int] = field(
         default_factory=lambda: {"train_shift": 5.0, "infer_shift": 5.0, "num_train_timesteps": 1000}
@@ -220,6 +237,8 @@ class FastWAMConfig(PreTrainedConfig):
         self.action_dit_config = self.action_dit_config or default_action_dit_config(self.action_dim)
         self.video_dit_config["fp32_attention"] = bool(self.fp32_attention)
         self.action_dit_config["fp32_attention"] = bool(self.fp32_attention)
+        self.video_dit_config["use_gradient_checkpointing"] = bool(self.use_gradient_checkpointing)
+        self.action_dit_config["use_gradient_checkpointing"] = bool(self.use_gradient_checkpointing)
         if self.input_features is None:
             height, width = self.image_size
             self.input_features = {
@@ -300,8 +319,28 @@ class FastWAMConfig(PreTrainedConfig):
             raise ValueError(f"`action_horizon` must be positive, got {self.action_horizon}.")
         if self.n_action_steps > self.action_horizon:
             raise ValueError("`n_action_steps` cannot exceed `action_horizon`.")
-        if self.num_video_frames % 4 != 1:
+        if self.action_video_freq_ratio <= 0:
-            raise ValueError(f"`num_video_frames` must satisfy T % 4 == 1, got {self.num_video_frames}.")
+            raise ValueError(
+                f"`action_video_freq_ratio` must be positive, got {self.action_video_freq_ratio}."
+            )
+        # Video frames are subsampled by action_video_freq_ratio; the resulting model frame
+        # count must satisfy T % 4 == 1 for the VAE temporal tokenization (mirrors the
+        # original FastWAM dataset asserts).
+        if (self.num_video_frames - 1) % self.action_video_freq_ratio != 0:
+            raise ValueError(
+                f"`num_video_frames - 1` ({self.num_video_frames - 1}) must be divisible by "
+                f"`action_video_freq_ratio` ({self.action_video_freq_ratio})."
+            )
+        if ((self.num_video_frames - 1) // self.action_video_freq_ratio) % 4 != 0:
+            raise ValueError(
+                f"Subsampled video transitions ({(self.num_video_frames - 1) // self.action_video_freq_ratio}) "
+                "must be divisible by 4 for VAE tokenization (i.e. model_video_frames % 4 == 1)."
+            )
+        if self.action_horizon % ((self.num_video_frames - 1) // self.action_video_freq_ratio) != 0:
+            raise ValueError(
+                f"`action_horizon` ({self.action_horizon}) must be divisible by the number of "
+                f"video transitions ({(self.num_video_frames - 1) // self.action_video_freq_ratio})."
+            )
         if not self.image_features:
             raise ValueError("FastWAM requires at least one image feature.")
         if self.action_feature is None:
@@ -333,8 +372,19 @@ class FastWAMConfig(PreTrainedConfig):
             raise ValueError(f"FastWAM image feature widths must sum to {width}, got {image_width_sum}.")
 
     @property
-    def observation_delta_indices(self) -> None:
+    def model_video_frames(self) -> int:
-        return None
+        """Number of video frames the model actually operates on, after subsampling the
+        raw `num_video_frames` window by `action_video_freq_ratio` (e.g. 33 -> 9)."""
+        return (self.num_video_frames - 1) // self.action_video_freq_ratio + 1
+
+    @property
+    def observation_delta_indices(self) -> list[int]:
+        # Load the video frames the model is supervised on: the future window subsampled by
+        # action_video_freq_ratio (e.g. [0, 4, 8, ..., 32] -> 9 frames). Each video frame is
+        # thus `action_video_freq_ratio` actions apart, while actions load at the full rate
+        # (`action_delta_indices` = range(action_horizon)). Returning None would load only the
+        # current frame, making the video target a static repeat (degenerate supervision).
+        return list(range(0, self.num_video_frames, self.action_video_freq_ratio))
 
     @property
     def action_delta_indices(self) -> list[int]:

src/lerobot/policies/fastwam/modeling_fastwam.py

@@ -15,7 +15,9 @@
 from __future__ import annotations
 
 import logging
+import os
 from collections import deque
+from pathlib import Path
 from typing import Any
 
 import torch
@@ -25,6 +27,23 @@ from lerobot.policies.pretrained import PreTrainedPolicy
 from lerobot.utils.constants import OBS_STATE
 
 from .configuration_fastwam import FastWAMConfig
+from .modular_fastwam import ActionDiT, FastWAM, MoT
+from .wan_components import (
+    build_wan_tokenizer,
+    load_pretrained_wan_text_encoder,
+    load_pretrained_wan_vae,
+)
+from .wan_video_dit import WanVideoDiT
+
+# TEMPORARY DEBUG — revert before merge. When FASTWAM_DECODE_DEBUG=1, route the first
+# eval episode's action chunks through `infer_joint` so the predicted video latents are
+# decoded by the VAE and dumped as PNG frames (sanity-checks the diffusers decode path).
+_FASTWAM_DECODE_DEBUG = os.environ.get("FASTWAM_DECODE_DEBUG") == "1"
+# Debug viz knob: extra divisor on the predicted-frame advance per env step. Should be 1
+# now that the model emits model_video_frames (so frames_per_step = (model_video_frames-1)/
+# action_horizon already encodes the action_video_freq_ratio). Was 4 to compensate for the
+# (now-fixed) bug where the model ran on the un-subsampled num_video_frames.
+_DEBUG_PRED_RATE_DIV = 1
 
 
 class FastWAMPolicy(PreTrainedPolicy):
@@ -43,13 +62,32 @@ class FastWAMPolicy(PreTrainedPolicy):
         self,
         config: FastWAMConfig,
         dataset_stats: dict[str, dict[str, Tensor]] | None = None,
+        **kwargs: Any,
     ):
+        # `make_policy`/`from_pretrained` forward extra kwargs (e.g. `dataset_meta`); the
+        # dataset feature metadata is already applied to `config` by make_policy upstream,
+        # so we accept and ignore them, matching the other LeRobot policies.
         super().__init__(config, dataset_stats)
         config.validate_features()
         self.config = config
         self.dataset_stats = dataset_stats
         self.model = self._build_core_model(config)
+        if config.freeze_video_expert and getattr(self.model, "video_expert", None) is not None:
+            # Freeze the ~5B Wan video expert; get_optim_params filters on requires_grad,
+            # so its params drop out of the optimizer (and DDP skips them).
+            self.model.video_expert.requires_grad_(False)
         self.reset()
+        # TEMPORARY DEBUG — revert before merge. Mark construction done so `reset()`
+        # counts only eval-rollout resets (one per episode), not this __init__ one.
+        self._debug_constructed = True
+        self._debug_episode_index = -1
+        self._debug_seen_tasks: set[str] = set()
+        self._debug_capturing = False
+        self._debug_episode_started = False
+        self._debug_episode_task = ""
+        self._debug_step_in_chunk = 0
+        self._debug_last_video: list | None = None
+        self._debug_pairs: list = []
 
     @classmethod
     def _load_as_safetensor(cls, model, model_file: str, map_location: str, strict: bool):
@@ -100,17 +138,33 @@ class FastWAMPolicy(PreTrainedPolicy):
             model.to(map_location)
         return model
 
-    def get_optim_params(self) -> dict[str, Any]:
+    def get_optim_params(self) -> list[Tensor]:
+        # Return the trainable tensors directly (a single param group). The optimizer
+        # builder wraps these in a param group; returning a bare {"params": [...]} dict
+        # instead would make `list(...)` yield the key string "params".
         params = (
             list(self.model.dit.parameters()) if hasattr(self.model, "dit") else list(self.model.parameters())
         )
         proprio_encoder = getattr(self.model, "proprio_encoder", None)
         if proprio_encoder is not None:
             params.extend(list(proprio_encoder.parameters()))
-        return {"params": [p for p in params if p.requires_grad]}
+        return [p for p in params if p.requires_grad]
 
     def reset(self) -> None:
         self._action_queue: deque[Tensor] = deque([], maxlen=self.config.n_action_steps)
+        # TEMPORARY DEBUG — revert before merge. Flush the just-finished episode's
+        # true-vs-pred video if it was a captured one (pairs accumulate only while
+        # capturing), then reset per-episode capture state.
+        if getattr(self, "_debug_constructed", False):
+            if _FASTWAM_DECODE_DEBUG and self._debug_pairs:
+                self._save_debug_video()
+            self._debug_episode_index += 1
+            self._debug_capturing = False
+            self._debug_episode_started = False
+            self._debug_episode_task = ""
+            self._debug_step_in_chunk = 0
+            self._debug_last_video = None
+            self._debug_pairs = []
 
     def _batch_to_training_sample(self, batch: dict[str, Tensor]) -> dict[str, Tensor]:
         """Adapt a standard LeRobot batch to the FastWAM-native sample that
@@ -144,7 +198,7 @@ class FastWAMPolicy(PreTrainedPolicy):
                 sample["proprio"] = state.unsqueeze(1) if state.ndim == 2 else state
         return sample
 
-    def forward(self, batch: dict[str, Tensor]) -> dict[str, Tensor]:
+    def forward(self, batch: dict[str, Tensor]) -> tuple[Tensor, dict[str, Any]]:
         """Compute FastWAM training loss for a LeRobot batch.
 
         Args:
@@ -154,19 +208,14 @@ class FastWAMPolicy(PreTrainedPolicy):
                 `action`, `action_is_pad`).
 
         Returns:
-            dict[str, Tensor]: Output dictionary containing the scalar `loss`
+            tuple[Tensor, dict[str, Any]]: The scalar loss to backprop, and a dict of
-            key required by LeRobot and optional tensor metrics.
+            logging metrics (e.g. `loss_video`, `loss_action`) — the `(loss, output_dict)`
+            contract the LeRobot training loop expects.
         """
 
         sample = self._batch_to_training_sample(batch)
         loss, metrics = self.model.training_loss(sample)
-        output = {"loss": loss}
+        return loss, dict(metrics or {})
-        for key, value in (metrics or {}).items():
-            if isinstance(value, Tensor):
-                output[key] = value.to(device=loss.device)
-            else:
-                output[key] = torch.as_tensor(value, device=loss.device)
-        return output
 
     @torch.no_grad()
     def predict_action_chunk(self, batch: dict[str, Tensor], **_: Any) -> Tensor:
@@ -183,7 +232,21 @@ class FastWAMPolicy(PreTrainedPolicy):
         self.eval()
         infer_kwargs = _batch_to_infer_kwargs(batch=batch, config=self.config)
         batch_size = _infer_kwargs_batch_size(infer_kwargs)
-        if batch_size == 1:
+        # TEMPORARY DEBUG — revert before merge. On captured episodes (first of each task),
+        # run the joint video+action path so the predicted video is VAE-decoded; stash it
+        # so select_action can pair each predicted frame with the real obs that follows.
+        if _FASTWAM_DECODE_DEBUG and getattr(self, "_debug_capturing", False) and batch_size == 1:
+            out = self.model.infer_joint(
+                **infer_kwargs,
+                num_video_frames=self.config.model_video_frames,
+                test_action_with_infer_action=False,
+            )
+            # The decoded rollout has model_video_frames frames spanning the full
+            # action_horizon (action_video_freq_ratio actions per frame); the per-step
+            # pairing indexes into it, so keep all frames.
+            self._debug_last_video = out["video"]
+            action = _action_from_model_output(out)
+        elif batch_size == 1:
             action = _action_from_model_output(self.model.infer_action(**infer_kwargs))
         else:
             action = torch.cat(
@@ -202,12 +265,98 @@ class FastWAMPolicy(PreTrainedPolicy):
     @torch.no_grad()
     def select_action(self, batch: dict[str, Tensor], **kwargs: Any) -> Tensor:
         self.eval()
+        # TEMPORARY DEBUG — revert before merge. On the first step of each episode, decide
+        # whether to capture: yes iff this episode's task hasn't been captured yet (so we
+        # get the first episode of every task).
+        if _FASTWAM_DECODE_DEBUG and not self._debug_episode_started:
+            self._debug_episode_started = True
+            task = self._debug_task_name(batch)
+            if task not in self._debug_seen_tasks:
+                self._debug_seen_tasks.add(task)
+                self._debug_capturing = True
+                self._debug_episode_task = task
+        capturing = _FASTWAM_DECODE_DEBUG and self._debug_capturing
         if len(self._action_queue) == 0:
             actions = self.predict_action_chunk(batch, **kwargs)[:, : self.config.n_action_steps]
             self._action_queue.extend(actions.transpose(0, 1))
+            if capturing:
+                self._debug_step_in_chunk = 0  # a fresh chunk was just predicted
+        if capturing:
+            self._debug_capture_pair(batch)
+            self._debug_step_in_chunk += 1
         return self._action_queue.popleft()
 
-    def _build_core_model(self, config: FastWAMConfig) -> torch.nn.Module:
+    # ---- TEMPORARY DEBUG (revert before merge): true-vs-predicted video capture ----
+    @staticmethod
+    def _debug_task_name(batch: dict[str, Any]) -> str:
+        task = batch.get("task")
+        if isinstance(task, (list, tuple)):
+            task = task[0] if task else None
+        return str(task) if task else "no_task"
+
+    def _debug_capture_pair(self, batch: dict[str, Tensor]) -> None:
+        video = getattr(self, "_debug_last_video", None)
+        if not video:
+            return
+        real = _input_image_from_batch(batch, self.config)[0]  # [C,H,W] in [-1,1]
+        # Map env-step offset within the chunk to a predicted-frame index. The rollout has
+        # (model_video_frames - 1) transitions over action_horizon actions, so each env step
+        # advances frames_per_step = (model_video_frames-1)/action_horizon frames (= 1/ratio,
+        # e.g. 8/32 = 0.25 — one predicted frame per ~4 actions).
+        frames_per_step = (self.config.model_video_frames - 1) / max(1, self.config.action_horizon)
+        idx = min(
+            int(round(self._debug_step_in_chunk * frames_per_step / _DEBUG_PRED_RATE_DIV)),
+            len(video) - 1,
+        )
+        pair = self._debug_hstack(self._debug_tensor_to_pil(real), video[idx])
+        self._debug_label_pair(pair, left_w=real.shape[-1], pred_idx=idx)
+        self._debug_pairs.append(pair)
+
+    @staticmethod
+    def _debug_label_pair(pair, left_w: int, pred_idx: int) -> None:
+        from PIL import ImageDraw
+
+        draw = ImageDraw.Draw(pair)
+        draw.text((3, 3), "true", fill=(255, 255, 0))
+        draw.text((left_w + 3, 3), f"pred[t+{pred_idx}]", fill=(0, 255, 0))
+
+    @staticmethod
+    def _debug_tensor_to_pil(image: Tensor):
+        from PIL import Image
+
+        arr = ((image.detach().float().clamp(-1.0, 1.0) + 1.0) * 127.5).to(torch.uint8)
+        return Image.fromarray(arr.cpu().permute(1, 2, 0).numpy())
+
+    @staticmethod
+    def _debug_hstack(left, right):
+        from PIL import Image
+
+        if right.height != left.height:
+            right = right.resize((round(right.width * left.height / right.height), left.height))
+        canvas = Image.new("RGB", (left.width + right.width, left.height))
+        canvas.paste(left, (0, 0))
+        canvas.paste(right, (left.width, 0))
+        return canvas
+
+    def _save_debug_video(self) -> None:
+        import re
+
+        import numpy as np
+
+        from lerobot.utils.io_utils import write_video
+
+        pairs = getattr(self, "_debug_pairs", None)
+        if not pairs:
+            return
+        out_dir = Path("outputs/fastwam_debug")
+        out_dir.mkdir(parents=True, exist_ok=True)
+        slug = re.sub(r"[^a-zA-Z0-9]+", "_", self._debug_episode_task).strip("_")[:40] or "task"
+        path = out_dir / f"ep{self._debug_episode_index:03d}_{slug}_true_vs_pred.mp4"
+        frames = [np.asarray(pair) for pair in pairs]  # HWC uint8 RGB
+        write_video(path, frames, fps=30)
+        logging.info("FASTWAM_DECODE_DEBUG: wrote %d-frame mp4 (left=true, right=pred) to %s", len(frames), path)
+
+    def _build_core_model(self, config: FastWAMConfig) -> FastWAM:
         """Build the FastWAM core for training / inference.
 
         Only the trainable parts (the MoT DiT and the proprio encoder) are
@@ -218,14 +367,6 @@ class FastWAMPolicy(PreTrainedPolicy):
         across checkpoints) and are intentionally excluded from `model.safetensors`
         — see `FastWAM.__init__`. The tokenizer comes from `google/umt5-xxl`.
         """
-        from .modular_fastwam import ActionDiT, FastWAM, MoT
-        from .wan_components import (
-            build_wan_tokenizer,
-            load_pretrained_wan_text_encoder,
-            load_pretrained_wan_vae,
-        )
-        from .wan_video_dit import WanVideoDiT
-
         dtype = _dtype_from_name(config.torch_dtype)
         device = config.device
         video_expert = WanVideoDiT(**config.video_dit_config).to(device=device, dtype=dtype)
@@ -342,15 +483,24 @@ def batch_device(batch: dict[str, Any]) -> torch.device:
 
 
 def _stack_video_from_images(batch: dict[str, Tensor], config: FastWAMConfig) -> Tensor:
-    image_keys = sorted(k for k in batch if k.startswith("observation.images."))
+    # Exclude the `*_is_pad` companion tensors that delta-timestamp loading adds alongside
+    # each camera (shape [B, T]); they share the `observation.images.` prefix but are not frames.
+    image_keys = sorted(
+        k for k in batch if k.startswith("observation.images.") and not k.endswith("_is_pad")
+    )
     if not image_keys:
         raise KeyError("FastWAM batch must contain `video` or `observation.images.*` keys.")
     images = [batch[key] for key in image_keys]
+    # Cameras concatenate along width (last dim) in both the single-frame and temporal case.
     image = torch.cat(images, dim=-1) if len(images) > 1 else images[0]
     if image.ndim == 4:
-        image = image.unsqueeze(2).repeat(1, 1, config.num_video_frames, 1, 1)
+        # [B, C, H, W]: a single frame (e.g. the live eval observation) -> repeat across time.
-    if image.ndim != 5:
+        image = image.unsqueeze(2).repeat(1, 1, config.model_video_frames, 1, 1)
-        raise ValueError(f"Expected image batch [B,C,H,W] or video [B,C,T,H,W], got {tuple(image.shape)}.")
+    elif image.ndim == 5:
+        # [B, T, C, H, W]: temporal stack from delta-timestamp loading -> [B, C, T, H, W].
+        image = image.permute(0, 2, 1, 3, 4)
+    else:
+        raise ValueError(f"Expected image batch [B,C,H,W] or temporal [B,T,C,H,W], got {tuple(image.shape)}.")
     return image
 
 

src/lerobot/policies/fastwam/processor_fastwam.py

@@ -42,6 +42,35 @@ from lerobot.utils.constants import (
 from .configuration_fastwam import FastWAMConfig
 
 
+@dataclass
+@ProcessorStepRegistry.register(name="fastwam_image_crop_resize_processor")
+class FastWAMImageCropResizeProcessorStep(ImageCropResizeProcessorStep):
+    """`ImageCropResizeProcessorStep` that tolerates a leading temporal/batch stack.
+
+    FastWAM loads a per-camera video stack, so image observations arrive as
+    ``[B, T, C, H, W]``. torchvision's crop/resize only accept ``[..., C, H, W]`` with a
+    single leading batch dim (resize raises on 5-D input), so we flatten any leading
+    dims into the batch, apply the base 4-D crop/resize, then restore the leading shape.
+    Crop/resize params and feature-shape bookkeeping are inherited unchanged.
+    """
+
+    def observation(self, observation: dict) -> dict:
+        leads: dict[str, tuple] = {}
+        flat_input = dict(observation)
+        for key, img in observation.items():
+            if "image" in key and torch.is_tensor(img) and img.ndim > 4:
+                leads[key] = tuple(img.shape[:-3])
+                flat_input[key] = img.reshape(-1, *img.shape[-3:])
+        processed = super().observation(flat_input)
+        if not leads:
+            return processed
+        out = dict(processed)
+        for key, lead in leads.items():
+            im = processed[key]
+            out[key] = im.reshape(*lead, *im.shape[-3:])
+        return out
+
+
 @dataclass
 @ProcessorStepRegistry.register(name="fastwam_action_toggle_processor")
 class FastWAMActionToggleProcessorStep(ActionProcessorStep):
@@ -111,7 +140,8 @@ def make_fastwam_pre_post_processors(
     resize_steps = []
     if visual_shapes:
         target_hw = (int(visual_shapes[0][1]), int(visual_shapes[0][2]))
-        resize_steps.append(ImageCropResizeProcessorStep(resize_size=target_hw))
+        # FastWAM-aware resize: tolerates the leading temporal dim of the video stack.
+        resize_steps.append(FastWAMImageCropResizeProcessorStep(resize_size=target_hw))
 
     input_steps = [
         RenameObservationsProcessorStep(rename_map={}),

src/lerobot/policies/fastwam/wan_components.py

@@ -20,12 +20,19 @@ from pathlib import Path
 from typing import TYPE_CHECKING, Any
 
 import torch
+from huggingface_hub import snapshot_download
 from safetensors.torch import load_file
+from transformers import AutoTokenizer, UMT5EncoderModel
 
 if TYPE_CHECKING:
     from .wan_adapters import WanVideoVAE38
     from .wan_video_dit import WanVideoDiT
 
+from diffusers import AutoencoderKLWan
+
+from .wan_adapters import WanVideoVAE38
+from .wan_video_dit import WanVideoDiT
+
 logger = logging.getLogger(__name__)
 
 # The custom MoT video DiT still ships in the original (non-diffusers) Wan2.2
@@ -65,8 +72,6 @@ class WanTokenizer:
     FastWAM call site expects."""
 
     def __init__(self, name: str = WAN_T5_TOKENIZER, seq_len: int = 512) -> None:
-        from transformers import AutoTokenizer
-
         self.tokenizer = AutoTokenizer.from_pretrained(name)
         self.seq_len = int(seq_len)
 
@@ -94,10 +99,6 @@ def build_wan_tokenizer(*, tokenizer_max_len: int) -> WanTokenizer:
 
 def load_pretrained_wan_vae(*, torch_dtype: torch.dtype, device: str) -> WanVideoVAE38:
     """Load real Wan2.2 VAE weights from the diffusers repo (offline base creation)."""
-    from diffusers import AutoencoderKLWan
-
-    from .wan_adapters import WanVideoVAE38
-
     vae = AutoencoderKLWan.from_pretrained(
         WAN22_DIFFUSERS_MODEL_ID, subfolder="vae", torch_dtype=torch_dtype
     )
@@ -106,8 +107,6 @@ def load_pretrained_wan_vae(*, torch_dtype: torch.dtype, device: str) -> WanVide
 
 def load_pretrained_wan_text_encoder(*, torch_dtype: torch.dtype, device: str) -> WanTextEncoder:
     """Load real UMT5-XXL encoder weights from the diffusers repo (offline base creation)."""
-    from transformers import UMT5EncoderModel
-
     encoder = UMT5EncoderModel.from_pretrained(
         WAN22_DIFFUSERS_MODEL_ID, subfolder="text_encoder", torch_dtype=torch_dtype
     )
@@ -126,8 +125,6 @@ def resolve_wan_dit_paths(
     if path.is_dir():
         return sorted(path.glob(WAN_DIT_PATTERN))
 
-    from huggingface_hub import snapshot_download
-
     snapshot_path = snapshot_download(
         repo_id=str(model_id_or_path),
         revision=revision,
@@ -145,8 +142,6 @@ def load_wan_video_dit(
     torch_dtype: torch.dtype,
     device: str,
 ) -> WanVideoDiT:
-    from .wan_video_dit import WanVideoDiT
-
     model = WanVideoDiT(**dit_config)
     state_dict = _read_wan_dit_safetensors(paths)
     model.load_state_dict(state_dict, strict=False)

src/lerobot/policies/fastwam/wan_video_dit.py

@@ -29,6 +29,7 @@ from .wan.modules.model import (
     rope_params,
     sinusoidal_embedding_1d,
 )
+from .wan.utils.fm_solvers import get_sampling_sigmas
 
 logger = logging.getLogger(__name__)
 
@@ -94,8 +95,6 @@ def modulate(x: torch.Tensor, shift: torch.Tensor, scale: torch.Tensor):
 
 
 def _get_wan_sampling_sigmas(num_inference_steps: int, shift: float) -> list[float]:
-    from .wan.utils.fm_solvers import get_sampling_sigmas
-
     return get_sampling_sigmas(num_inference_steps, shift)
 
 

tests/policies/fastwam/test_fastwam_policy.py

@@ -49,6 +49,8 @@ def test_fastwam_is_registered_and_publicly_exported():
         proprio_dim=2,
         action_horizon=4,
         n_action_steps=2,
+        num_video_frames=5,
+        action_video_freq_ratio=1,
         base_model_id=None,
     )
 
@@ -78,6 +80,8 @@ def test_preprocessor_normalizes_images_and_postprocessor_toggles_actions(tmp_pa
         proprio_dim=2,
         action_horizon=4,
         n_action_steps=2,
+        num_video_frames=5,
+        action_video_freq_ratio=1,
         image_size=(2, 2),
         device="cpu",
         toggle_action_dimensions=[-1],
@@ -154,6 +158,8 @@ def test_policy_forward_and_predict_action_adapt_lerobot_batches(monkeypatch):
         proprio_dim=2,
         action_horizon=4,
         n_action_steps=2,
+        num_video_frames=5,
+        action_video_freq_ratio=1,
         image_size=(16, 16),
         input_features={
             "observation.images.image": PolicyFeature(type=FeatureType.VISUAL, shape=(3, 16, 16)),
@@ -164,7 +170,7 @@ def test_policy_forward_and_predict_action_adapt_lerobot_batches(monkeypatch):
     )
     policy = FastWAMPolicy(cfg)
 
-    output = policy.forward(
+    loss, metrics = policy.forward(
         {
             "observation.images.image": torch.zeros(1, 3, 16, 16),
             OBS_STATE: torch.zeros(1, 2),
@@ -186,8 +192,8 @@ def test_policy_forward_and_predict_action_adapt_lerobot_batches(monkeypatch):
         }
     )
 
-    assert output["loss"].item() == 1.0
+    assert loss.item() == 1.0
-    assert output["loss_action"].item() == 1.0
+    assert metrics["loss_action"] == 1.0
     assert action.shape == (2, 4, 3)
     assert action[:, 0, 0].tolist() == [1.0, 2.0]
     assert [item["image_shape"] for item in captured] == [(1, 3, 16, 16), (1, 3, 16, 16)]
@@ -218,7 +224,7 @@ class CoreWithFrozenComponents(FakeFastWAMCore):
 
 
 def test_from_pretrained_uses_base_loader_and_skips_wan_backbone(monkeypatch, tmp_path):
-    cfg = FastWAMConfig(action_dim=3, proprio_dim=2, action_horizon=4, n_action_steps=2, base_model_id=None)
+    cfg = FastWAMConfig(action_dim=3, proprio_dim=2, action_horizon=4, n_action_steps=2, num_video_frames=5, action_video_freq_ratio=1, base_model_id=None)
 
     def build_core(self, config):
         core = CoreWithFrozenComponents()
@@ -250,7 +256,7 @@ def test_from_pretrained_uses_base_loader_and_skips_wan_backbone(monkeypatch, tm
 
 
 def test_save_pretrained_excludes_frozen_components(monkeypatch, tmp_path):
-    cfg = FastWAMConfig(action_dim=3, proprio_dim=2, action_horizon=4, n_action_steps=2, base_model_id=None)
+    cfg = FastWAMConfig(action_dim=3, proprio_dim=2, action_horizon=4, n_action_steps=2, num_video_frames=5, action_video_freq_ratio=1, base_model_id=None)
     monkeypatch.setattr(FastWAMPolicy, "_build_core_model", lambda self, config: CoreWithFrozenComponents())
     policy = FastWAMPolicy(cfg)
 
@@ -272,7 +278,7 @@ def test_save_pretrained_excludes_frozen_components(monkeypatch, tmp_path):
 
 
 def test_frozen_components_excluded_from_params_but_follow_device_moves(monkeypatch):
-    cfg = FastWAMConfig(action_dim=3, proprio_dim=2, action_horizon=4, n_action_steps=2, base_model_id=None)
+    cfg = FastWAMConfig(action_dim=3, proprio_dim=2, action_horizon=4, n_action_steps=2, num_video_frames=5, action_video_freq_ratio=1, base_model_id=None)
     monkeypatch.setattr(FastWAMPolicy, "_build_core_model", lambda self, config: CoreWithFrozenComponents())
     policy = FastWAMPolicy(cfg)