fix: Windows stability issues (console encoding, camera enumeration, …

lelab/record.py

@@ -23,6 +23,7 @@
 from pydantic import BaseModel
 
 from lerobot.configs.dataset import DatasetRecordConfig
+from lerobot.configs.video import RGBEncoderConfig
 from lerobot.datasets import LeRobotDataset
 from lerobot.robots.so_follower import SO101FollowerConfig
 
@@ -183,6 +184,10 @@ def create_record_config(request: RecordingRequest) -> RecordConfig:
         tags=with_lelab_tag(request.tags) if request.push_to_hub else None,
         private=request.private,
         streaming_encoding=request.streaming_encoding,
+        # libsvtav1 (lerobot's default) is CPU-heavy enough on this machine to starve
+        # the motor bus read loop mid-recording ("no status packet" ConnectionError,
+        # see 2026-07-15 crashes). h264/ultrafast measured ~11x faster to encode here.
+        rgb_encoder=RGBEncoderConfig(vcodec="h264", preset="ultrafast"),
     )
 
     # Create the main record config
@@ -309,11 +314,15 @@ def recording_worker():
                     "robot_type": getattr(dataset.meta, "robot_type", "Unknown robot"),
                 }
             except Exception as e:
-                logger.exception("Recording session failed")
+                logger.exception("Recording session failed: %r", e)
                 current_phase = "error"
                 if recording_start_time:
                     session_end_elapsed_seconds = int(time.time() - recording_start_time)
-                last_recording_info = {"success": False, "error": str(e)}
+                last_recording_info = {
+                    "success": False,
+                    "error": str(e) or repr(e),
+                    "dataset_repo_id": request.dataset_repo_id,
+                }
             finally:
                 if current_phase != "error":
                     current_phase = "completed"
@@ -419,7 +428,11 @@ def handle_recording_status() -> dict[str, Any]:
             "rerecord_episode": recording_active
             and current_phase == "recording",  # Only during recording phase
         },
-        "message": "Recording session failed with error - check logs"
+        "message": (
+            f"Recording failed: {last_recording_info['error']}"
+            if last_recording_info and last_recording_info.get("error")
+            else "Recording session failed with error - check logs"
+        )
         if current_phase == "error"
         else (
             "Recording session has ended - stop polling"

lelab/server.py

@@ -36,6 +36,15 @@
 from starlette.responses import Response
 from starlette.types import Scope
 
+# Windows consoles often use a legacy code page (cp1252) that can't encode the
+# emoji used in log/print output; an unhandled UnicodeEncodeError inside an
+# endpoint then turns into a 500 and hides the real error from the frontend.
+# Replace unencodable characters instead of crashing.
+for _stream in (sys.stdout, sys.stderr):
+    if _stream is not None and hasattr(_stream, "reconfigure"):
+        with contextlib.suppress(Exception):
+            _stream.reconfigure(errors="replace")
+
 from . import datasets as dataset_browser
 
 # Import our custom calibration functionality
@@ -998,6 +1007,18 @@ def _windows_cameras() -> list[dict[str, Any]]:
     frontend match each index to the browser's ``MediaDeviceInfo.label`` for the
     live preview. Falls back to generic names if pygrabber is unavailable.
     """
+    # pygrabber uses COM, which must be initialized per-thread. FastAPI serves
+    # sync endpoints from a thread pool whose threads never call CoInitialize,
+    # so enumeration fails intermittently depending on which thread handles the
+    # request. Initialize COM here and balance with CoUninitialize.
+    import ctypes
+
+    com_initialized = False
+    try:
+        hr = ctypes.windll.ole32.CoInitialize(None)
+        com_initialized = hr in (0, 1)  # S_OK or S_FALSE (already initialized)
+    except Exception:
+        pass
     try:
         from pygrabber.dshow_graph import FilterGraph
 
@@ -1007,6 +1028,9 @@ def _windows_cameras() -> list[dict[str, Any]]:
         import cv2
 
         return _generic_cv2_cameras(cv2.CAP_DSHOW)
+    finally:
+        if com_initialized:
+            ctypes.windll.ole32.CoUninitialize()
     return [{"index": i, "name": name, "available": True} for i, name in enumerate(names)]