fix(videovla): improve PerceiverResampler and address code review issues

Key fixes for the PI05Video policy implementation:

PerceiverResampler improvements:
- Add residual connection (latents + attn_out) for better gradient flow
- Add output LayerNorm after residual connection
- Initialize latents with smaller variance (*0.02) for stability

Bug fixes:
- Replace expand() with repeat() in _preprocess_video to create copies
  instead of memory views, preventing potential in-place modification bugs
- Fix dtype consistency in embed_video: use PaliGemma's dtype instead
  of input dtype for consistent processing throughout the pipeline
- Add bfloat16/float16 support to resize_with_pad_torch

PEFT improvements:
- Remove state_proj from target modules (PI0-only, not in PI05)
- Add video_proj and video_resampler to PEFT targets for fine-tuning

Other improvements:
- Add warning when use_video_encoder=True but no image features found
- Add gradient checkpointing support for video encoder
- Remove duplicate tokenizer_max_length definition in config
- Add validation for video_num_latents and video_resampler_num_heads

src/lerobot/policies/videovla/configuration_pi05.py

@@ -108,8 +108,6 @@ class PI05VideoConfig(PreTrainedConfig):
     scheduler_decay_steps: int = 30_000
     scheduler_decay_lr: float = 2.5e-6
 
-    tokenizer_max_length: int = 200  # see openpi `__post_init__`
-
     def __post_init__(self):
         super().__post_init__()
 
@@ -138,6 +136,12 @@ class PI05VideoConfig(PreTrainedConfig):
                 raise ValueError(
                     f"video_padding_mode must be 'repeat' or 'zero', got {self.video_padding_mode}"
                 )
+            if self.video_num_latents < 1:
+                raise ValueError(f"video_num_latents must be >= 1, got {self.video_num_latents}")
+            if self.video_resampler_num_heads < 1:
+                raise ValueError(
+                    f"video_resampler_num_heads must be >= 1, got {self.video_resampler_num_heads}"
+                )
 
     def validate_features(self) -> None:
         """Validate and set up input/output features."""

src/lerobot/policies/videovla/modeling_pi05.py

@@ -197,7 +197,7 @@ def resize_with_pad_torch(  # see openpi `resize_with_pad_torch` (exact copy)
     # Handle dtype-specific clipping
     if images.dtype == torch.uint8:
         resized_images = torch.round(resized_images).clamp(0, 255).to(torch.uint8)
-    elif images.dtype == torch.float32:
+    elif images.dtype in (torch.float32, torch.float16, torch.bfloat16):
         resized_images = resized_images.clamp(-1.0, 1.0)
     else:
         raise ValueError(f"Unsupported image dtype: {images.dtype}")
@@ -315,8 +315,8 @@ class PerceiverResampler(nn.Module):
         self.num_latents = num_latents
         self.dim = dim
 
-        # Learnable query tokens
-        self.latents = nn.Parameter(torch.randn(num_latents, dim))
+        # Learnable query tokens (initialized with small values for stability)
+        self.latents = nn.Parameter(torch.randn(num_latents, dim) * 0.02)
 
         # Cross-attention layer
         self.attn = nn.MultiheadAttention(
@@ -328,6 +328,8 @@ class PerceiverResampler(nn.Module):
         # Layer norms for queries and key-values
         self.ln_q = nn.LayerNorm(dim)
         self.ln_kv = nn.LayerNorm(dim)
+        # Output layer norm (applied after residual connection)
+        self.ln_out = nn.LayerNorm(dim)
 
     def forward(self, x: torch.Tensor) -> torch.Tensor:
         """
@@ -347,7 +349,10 @@ class PerceiverResampler(nn.Module):
         kv = self.ln_kv(x)
 
         # Cross-attention: queries attend to video tokens
-        out, _ = self.attn(q, kv, kv, need_weights=False)  # (B, num_latents, D)
+        attn_out, _ = self.attn(q, kv, kv, need_weights=False)  # (B, num_latents, D)
+
+        # Residual connection + output layer norm
+        out = self.ln_out(latents + attn_out)
 
         return out
 
@@ -693,6 +698,13 @@ class PI05Pytorch(nn.Module):  # see openpi `PI0Pytorch`
         self.paligemma_with_expert.paligemma.language_model.gradient_checkpointing = True
         self.paligemma_with_expert.paligemma.vision_tower.gradient_checkpointing = True
         self.paligemma_with_expert.gemma_expert.model.gradient_checkpointing = True
+
+        # Enable gradient checkpointing for video encoder if available and not frozen
+        if self.video_encoder is not None and not self.config.freeze_video_encoder:
+            if hasattr(self.video_encoder, "gradient_checkpointing_enable"):
+                self.video_encoder.gradient_checkpointing_enable()
+                logging.info("Enabled gradient checkpointing for video encoder")
+
         logging.info("Enabled gradient checkpointing for PI05Pytorch model")
 
     def gradient_checkpointing_disable(self):
@@ -701,6 +713,13 @@ class PI05Pytorch(nn.Module):  # see openpi `PI0Pytorch`
         self.paligemma_with_expert.paligemma.language_model.gradient_checkpointing = False
         self.paligemma_with_expert.paligemma.vision_tower.gradient_checkpointing = False
         self.paligemma_with_expert.gemma_expert.model.gradient_checkpointing = False
+
+        # Disable gradient checkpointing for video encoder if available
+        if self.video_encoder is not None:
+            if hasattr(self.video_encoder, "gradient_checkpointing_disable"):
+                self.video_encoder.gradient_checkpointing_disable()
+                logging.info("Disabled gradient checkpointing for video encoder")
+
         logging.info("Disabled gradient checkpointing for PI05Pytorch model")
 
     def _rtc_enabled(self):
@@ -807,13 +826,15 @@ class PI05Pytorch(nn.Module):  # see openpi `PI0Pytorch`
 
         Returns:
             Video embeddings of shape [B, num_video_tokens, hidden_dim] projected to
-            PaliGemma's hidden dimension.
+            PaliGemma's hidden dimension, in the same dtype as PaliGemma's language model.
         """
         if self.video_encoder is None:
             raise RuntimeError("Video encoder is not initialized. Set use_video_encoder=True in config.")
 
         device = video_frames.device
-        dtype = video_frames.dtype
+
+        # Determine target dtype: match PaliGemma's language model dtype for consistency
+        paligemma_dtype = self.paligemma_with_expert.paligemma.language_model.embed_tokens.weight.dtype
 
         # Move video encoder to the same device if needed
         if next(self.video_encoder.parameters()).device != device:
@@ -848,8 +869,8 @@ class PI05Pytorch(nn.Module):  # see openpi `PI0Pytorch`
             # Shape: [B, num_patches * num_frames, hidden_size] (e.g., [B, 4096, 768])
             video_embeddings = video_outputs.last_hidden_state
 
-        # Convert to working dtype
-        video_embeddings = video_embeddings.to(dtype=dtype)
+        # Convert to PaliGemma's dtype for consistency with the rest of the model
+        video_embeddings = video_embeddings.to(dtype=paligemma_dtype)
 
         # Apply Perceiver Resampler to reduce tokens (e.g., 4096 -> 128)
         # This uses cross-attention from learnable queries to the video tokens
@@ -1369,6 +1390,12 @@ class PI05VideoPolicy(PreTrainedPolicy):
         if self.config.image_features:
             return next(iter(self.config.image_features.keys()))
 
+        # Warn if video encoder is enabled but no image features found
+        logging.warning(
+            "use_video_encoder=True but no image features found in config. "
+            "Video encoding will be skipped. Either set video_encoder_camera_key "
+            "or ensure image_features contains at least one camera."
+        )
         return None
 
     def _preprocess_images(self, batch: dict[str, Tensor]) -> tuple[list[Tensor], list[Tensor]]:
@@ -1496,7 +1523,9 @@ class PI05VideoPolicy(PreTrainedPolicy):
             # Single frame [B, C, H, W] - expand to video by repeating
             B, C, H, W = img.shape
             if self.config.video_padding_mode == "repeat":
-                video_frames = img.unsqueeze(1).expand(B, self.config.video_num_frames, C, H, W)
+                # Use repeat() instead of expand() to create actual copies, not views
+                # This prevents potential issues if downstream operations modify tensors in-place
+                video_frames = img.unsqueeze(1).repeat(1, self.config.video_num_frames, 1, 1, 1)
             else:  # zero padding
                 video_frames = torch.zeros(
                     B, self.config.video_num_frames, C, H, W, dtype=img.dtype, device=img.device
@@ -1513,8 +1542,9 @@ class PI05VideoPolicy(PreTrainedPolicy):
 
                 if self.config.video_padding_mode == "repeat":
                     # Repeat the first frame to fill missing frames at the beginning
+                    # Use repeat() instead of expand() to create actual copies, not views
                     first_frame = video_frames[:, 0:1]  # [B, 1, C, H, W]
-                    padding = first_frame.expand(B, num_missing, C, H, W)
+                    padding = first_frame.repeat(1, num_missing, 1, 1, 1)
                     video_frames = torch.cat([padding, video_frames], dim=1)
                 else:  # zero padding
                     # Zero-pad at the beginning
@@ -1625,11 +1655,21 @@ class PI05VideoPolicy(PreTrainedPolicy):
             return loss, loss_dict
 
     def _get_default_peft_targets(self) -> dict[str, any]:
-        """Return default PEFT target modules for PI0.5 fine-tuning."""
-        common_projections = (
-            "state_proj|action_in_proj|action_out_proj|action_time_mlp_in|action_time_mlp_out"
-        )
-        target_modules = rf"(.*\.gemma_expert\..*\.self_attn\.(q|v)_proj|model\.({common_projections}))"
+        """Return default PEFT target modules for PI0.5 fine-tuning.
+
+        Note: PI05 does NOT have state_proj (that's PI0 only). PI05 tokenizes state
+        into the language prompt instead.
+        """
+        # Core PI05 projections (no state_proj in PI05)
+        core_projections = "action_in_proj|action_out_proj|time_mlp_in|time_mlp_out"
+
+        # Video-related modules (only present if use_video_encoder=True)
+        video_projections = "video_proj|video_resampler\\..*"
+
+        # Combine all projections
+        all_projections = f"{core_projections}|{video_projections}"
+
+        target_modules = rf"(.*\.gemma_expert\..*\.self_attn\.(q|v)_proj|model\.({all_projections}))"
         return {
             "target_modules": target_modules,
             "modules_to_save": [],