Resolved critical issue where compression jobs would get stuck at random
progress percentages (e.g., 35.5%) due to pipe buffer deadlock.
**Root Cause:**
- Python code only read ffmpeg's stdout for progress updates
- ffmpeg's stderr pipe buffer (64KB) would fill with output
- ffmpeg blocked writing to stderr, Python blocked reading stdout
- Result: deadlock with job appearing stuck but ffmpeg still using CPU
**Fixes:**
- Read stdout and stderr concurrently using asyncio.gather()
- Prevents pipe buffer deadlock by consuming both streams
- Added watchdog timer to detect genuinely stuck jobs (5 min timeout)
- Improved error logging with stderr capture
- Better error messages showing exact failure reason
**Additional Improvements:**
- Watchdog sets job.error with informative message before killing
- Captures last 50 lines of stderr on failure for debugging
- Enhanced cancellation handling with multiple checkpoints
Tested with previously stuck video file - progress now updates
continuously throughout encoding process.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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