Why Extract Audio from a Lecture Video?
Video files recorded by Zoom, Teams, Meet, or a screen recorder are typically 10-20x larger than their audio tracks. A 90-minute lecture recorded at 1080p might be 1.2 GB. The same lecture as a 192 kbps MP3 is about 130 MB — nearly 10x smaller.Why this matters practically:
- Offline listening: MP3 files work in every audio player, including offline capable apps. Video files require more battery and storage.
- Transcription: Audio-to-text services are optimized for MP3 input. Sending a 1.2 GB video to a transcription service is slower and more expensive than sending a 130 MB MP3.
- Storage: Keeping 20 lecture recordings as MP3 instead of MP4 saves roughly 20 GB of storage.
Recording Sources and File Types
| Recording source | Typical file type | Supported? |
|---|---|---|
| Zoom cloud recording | .mp4 | Yes |
| Microsoft Teams | .mp4 | Yes |
| Google Meet (downloaded) | .mp4 | Yes |
| OBS Studio | .mp4, .mkv, .mov | Yes |
| QuickTime screen recording | .mov | Yes |
| iPhone screen recording | .mp4 | Yes |
The MP4 to MP3 converter uses ffmpeg.wasm with the full FFmpeg demuxer library — all of the above container formats are supported.
After Extracting: Transcription Options
Free option — Google Docs voice typing:- Upload the MP3 to Google Drive
- Right-click, Open with Google Docs
- Google automatically transcribes the audio
Real-time during meetings — Otter.ai: Integrates with Zoom and Teams to generate transcripts in real time. The free tier covers ~300 minutes/month.