Refactor: Consolidate duplicate functions in Python codebase

[skywinder]

Summary

Code review identified several duplicate function implementations across the Python codebase that should be consolidated into shared modules.

True Duplicates (should be consolidated)

1. wav_to_array - Exact duplicate

• Locations: whisper_server/server.py:49 and chunking.py:74
• Description: Nearly identical code for converting WAV to numpy array
• Recommendation: Extract to lib/audio.py

2. read_codec - Exact duplicate

• Locations: whisper_server/server.py:67 and chunking.py:119
• Description: Nearly identical code for reading audio codecs via ffmpeg
• Recommendation: Extract to lib/audio.py

3. combine_chunks_to_wav - Similar implementation

• Locations: diarization_worker.py:196 and play.py:103
• Description: Both combine opus chunks into WAV with gap/silence handling
• Recommendation: Extract common logic to shared module

4. mongo_cursor - Duplicate in playground

• Locations: lib/worker.py:52 (shared utility) and playground.local.py:16
• Recommendation: The playground version should import from lib/worker

Similar but different (may be intentional)

5. format_eta / _format_eta

• stt.py:167 returns "02:15:30" format
• diarization_worker.py:127 returns "0:15:30" (timedelta string)
• Note: Different output formats - may be intentional

6. get_worker_id / _get_worker_id

• lib/worker.py:47 returns "hostname_pid"
• processors/vad.py:35 returns "py-vad:hostname:pid" (different prefix)
• Note: Different formats to distinguish worker types - likely intentional

Proposed Solution

1. Create lib/audio.py with shared audio functions (wav_to_array, read_codec, potentially combine_chunks_to_wav)
2. Update whisper_server/server.py and chunking.py to import from lib/audio.py
3. Fix playground.local.py to import mongo_cursor from lib/worker
4. Consider consolidating format_eta functions if consistent output format is acceptable

Benefits

• Reduced code duplication
• Single source of truth for audio processing utilities
• Easier maintenance and bug fixes