Merge pull request #40 from nerdymark/claude/claude-md-mmikl14iywxsip5l-EbCmh F... 

File: backend/timelapse.py
 import shutil
 import subprocess
 import tempfile
+import threading
 from pathlib import Path
 from typing import Optional
 def generate_timelapse(
             text=True,
         )
+        # Drain stderr in a background thread to prevent pipe buffer
+        # deadlock.  ffmpeg writes status/errors to stderr; if the
+        # 64 KB pipe buffer fills while we're blocking on stdout
+        # readline, ffmpeg stalls and the job hangs forever.
+        stderr_lines: list[str] = []
+
+        def _drain_stderr():
+            for line in proc.stderr:
+                stderr_lines.append(line)
+
+        stderr_thread = threading.Thread(target=_drain_stderr, daemon=True)
+        stderr_thread.start()
+
         # Parse ffmpeg progress output
         frames_done = 0
         while True:
             if cancel_check and cancel_check():
                 proc.kill()
                 proc.wait()
+                stderr_thread.join(timeout=5)
                 if output_path.exists():
                     output_path.unlink()
                 raise RuntimeError("Timelapse generation cancelled")
 def generate_timelapse(
                     pass
         proc.wait()
+        stderr_thread.join(timeout=10)
         if proc.returncode != 0:
-            stderr = proc.stderr.read()
+            stderr = "".join(stderr_lines)
             logger.error("ffmpeg failed (rc=%d): %s", proc.returncode, stderr)
             if output_path.exists():
                 output_path.unlink()
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