FIXES:
- Fixed --tiny --nvhevc to use MP4 container instead of WEBM
- Added conflict detection for --x264 and --nvhevc flags
- Fixed stats system to accumulate data properly (total_files, total_time, average_time)
- Improved error handling for missing flag values
IMPROVEMENTS:
- Implemented actual progress tracking using FFmpeg stderr parsing
- Added real-time progress bar with ETA calculation
- Progress shows percentage complete and estimated time remaining
- Stats now properly accumulate over time instead of overwriting
TECHNICAL:
- Added bufio import for progress parsing
- Enhanced container compatibility logic
- Better error messages for conflicting flags
- Improved stats JSON structure with proper data types
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