Enhance file selection to support additional audio format (M4A) and update README.md to reflect new supported formats for video and audio recordings.

M4A-SUPPORT.md

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+# 🎵 M4A Audio File Support
+
+VideoTranscriber now supports M4A audio files! This format is commonly used by:
+- Apple devices (iPhone, iPad, Mac)
+- Voice recording apps
+- Audio podcasts and interviews
+- High-quality audio recordings
+
+## What's New
+
+### Supported Formats
+- **Video**: MP4, AVI, MOV, MKV
+- **Audio**: M4A ✨ (NEW!)
+
+### How It Works
+
+1. **Direct Processing**: M4A files are processed directly without audio extraction
+2. **Same Features**: All transcription and summarization features work with M4A
+3. **Optimized Performance**: Faster processing since no video-to-audio conversion needed
+
+## Usage Examples
+
+### Common M4A Sources
+
+#### iPhone Voice Memos
+```
+/Users/yourname/Desktop/recordings/
+├── meeting_notes.m4a
+├── interview.m4a
+└── lecture.m4a
+```
+
+#### Podcast Recordings
+```
+/path/to/podcast/
+├── episode_001.m4a
+├── episode_002.m4a
+└── bonus_content.m4a
+```
+
+#### Professional Audio
+```
+/path/to/audio/
+├── conference_call.m4a
+├── client_interview.m4a
+└── webinar_recording.m4a
+```
+
+## Technical Details
+
+### File Processing
+- **M4A Files**: Processed directly by Whisper (no conversion needed)
+- **Video Files**: Audio extracted first, then processed
+- **Performance**: M4A processing is faster due to no extraction step
+
+### Quality Considerations
+- M4A supports high-quality audio compression
+- Better quality = more accurate transcription
+- Recommended: 44.1kHz, 16-bit or higher
+
+### Supported Features with M4A
+- ✅ **Transcription**: Full Whisper model support
+- ✅ **Summarization**: Ollama and HuggingFace models
+- ✅ **Speaker Diarization**: Identify different speakers
+- ✅ **Translation**: Multi-language support
+- ✅ **Keyword Extraction**: Important terms with timestamps
+- ✅ **Export Formats**: SRT, ASS, VTT subtitles
+- ✅ **Caching**: Faster re-processing
+
+## Getting Started
+
+1. **Place M4A files** in your designated recordings folder
+2. **Launch VideoTranscriber**
+3. **Select folder** containing your M4A files
+4. **Choose file** from dropdown (M4A files will appear alongside videos)
+5. **Process** as normal - all features work identically!
+
+## Troubleshooting
+
+### M4A Files Not Appearing
+- Check file extension is `.m4a` (lowercase)
+- Ensure files are in the selected folder
+- Verify no file corruption
+
+### Processing Issues
+- M4A files with DRM protection may not work
+- Very large files (>2GB) may need more memory
+- Ensure FFmpeg is properly installed
+
+### Quality Issues
+- Low-quality recordings may have poor transcription
+- Background noise affects accuracy
+- Consider noise reduction before processing
+
+## Comparison: M4A vs Video Files
+
+| Feature | M4A Files | Video Files |
+|---------|-----------|-------------|
+| Processing Speed | ⚡ Faster | Slower (audio extraction needed) |
+| File Size | 📦 Smaller | Larger |
+| Quality | 🎵 Audio-optimized | May have video artifacts |
+| Compatibility | ✅ Direct support | ✅ Supported (via extraction) |
+| Use Cases | Interviews, podcasts, meetings | Screen recordings, presentations |
+
+## Future Enhancements
+
+Planned improvements for audio file support:
+- Additional audio formats (WAV, FLAC, AAC)
+- Batch processing for multiple M4A files
+- Audio quality analysis and optimization suggestions
+- Integration with cloud audio services
+
+---
+
+M4A support makes VideoTranscriber more versatile for pure audio content while maintaining all the powerful transcription and analysis features you expect!