Default DataLoader multiprocessing context to spawn

src/lerobot/configs/train.py

@@ -99,6 +99,14 @@ class TrainPipelineConfig(HubMixin):
     batch_size: int = 8
     prefetch_factor: int = 4
     persistent_workers: bool = True
+    # DataLoader multiprocessing start method. "spawn" is the safe default on
+    # Linux because workers do not inherit fork-time state from the parent —
+    # "fork" can crash with non-fork-safe libraries that the parent has loaded
+    # (e.g. PyAV / torchcodec / ffmpeg) with errors like
+    # `multiprocessing.context.AuthenticationError: digest received was wrong`,
+    # `Pin memory thread exited unexpectedly`, or random worker segfaults.
+    # See https://github.com/huggingface/lerobot/issues/2488.
+    dataloader_multiprocessing_context: str = "spawn"
     steps: int = 100_000
     eval_freq: int = 20_000
     log_freq: int = 200

src/lerobot/scripts/lerobot_train.py

@@ -411,6 +411,7 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
         drop_last=False,
         prefetch_factor=cfg.prefetch_factor if cfg.num_workers > 0 else None,
         persistent_workers=cfg.persistent_workers and cfg.num_workers > 0,
+        multiprocessing_context=cfg.dataloader_multiprocessing_context if cfg.num_workers > 0 else None,
     )
 
     # Prepare everything with accelerator