Quick start: extract audio from any video
- Select your video — Drag and drop MP4, MOV, WebM, AVI, MKV, or M4A. ffmpeg.wasm reads the container header first.
- Conversion runs locally — FFmpeg demuxes the video stream, re-encodes audio to 192 kbps MP3 via the built-in LAME encoder.
- Download the MP3 — Click Download when the progress bar hits 100%. Named after your source file.
How ffmpeg.wasm works in your browser
This tool runs ffmpeg.wasm — a full WebAssembly port of the FFmpeg multimedia framework — directly inside your browser tab. FFmpeg is the same open-source engine used by VLC, Handbrake, and YouTube's internal processing pipeline. The WASM build (~25 MB core + codec libraries) loads once on first use; everything after that runs on your CPU without touching the network.The conversion pipeline
| Step | FFmpeg operation | Detail |
|---|---|---|
| 1. Load | ffmpeg.wasm initialises in a Web Worker | ~25 MB WASM binary cached after first visit |
| 2. Demux | Container parser reads MP4/MOV/MKV structure | Detects audio codec (AAC, MP3, Opus, PCM, etc.) |
| 3. Strip | Video stream discarded entirely | Only audio packets are passed forward |
| 4. Decode | Audio packets decoded to raw PCM samples | Sample rate and channel layout preserved |
| 5. Encode | LAME encoder writes 192 kbps CBR MP3 | Constant bitrate — predictable file size |
| 6. Export | MP3 written to in-browser virtual FS | Triggered as a browser download blob |
All steps run inside a Web Worker — the main UI thread stays responsive while a 45-minute lecture converts in the background.
Supported containers and codecs
| Container | Common audio codecs | Supported |
|---|---|---|
| MP4 | AAC, MP3 | Yes |
| MOV | AAC, PCM | Yes |
| WebM | Opus, Vorbis | Yes |
| MKV | AAC, FLAC, MP3 | Yes |
| AVI | MP3, PCM | Yes |
| M4A | AAC (audio-only) | Yes |
| FLV | MP3, AAC | Yes |
RAM sizing guide
Because ffmpeg.wasm processes files in memory (not streaming from disk), available RAM is the practical limit:| Video file size | Recommended device | Expected result |
|---|---|---|
| Under 100 MB | Any modern phone or laptop | Works smoothly |
| 100–500 MB | Desktop/laptop with 8 GB+ RAM | Works well |
| 500 MB–1 GB | Desktop with 16 GB+ RAM | Usually works |
| Over 1 GB | High-RAM desktop only | May fail on low-memory devices |
On phones, keep files under 200–300 MB for reliable conversion.
Why ffmpeg.wasm vs a cloud converter
Most online video converters upload your file to a server, process it remotely, and serve back a download link. That means upload wait time proportional to file size, free-tier caps at 100–500 MB, and privacy exposure — the service has access to your video content.With ffmpeg.wasm running locally, conversion speed is limited only by your CPU, not your internet connection. A 20-minute lecture that might take 3 minutes to upload converts to MP3 in ~15 seconds locally on a mid-range laptop.
Practical use cases
Podcast and lecture archiving: Record a Zoom call or screen capture, drop the video here, and extract the audio for transcription or podcast distribution.Music and sound design: Extract audio from video clips for background music, sound effects, or sample material. 192 kbps retains all frequency detail needed for mixing.
Storage optimization: Video files are 5–20× larger than their audio tracks. If you only need the audio going forward, extract the MP3 and delete the heavy source file.