How to Extract Audio from a Video (MP4 to MP3 in Your Browser)
You have a video. You don't want the picture, you want the sound. Maybe it's a Zoom recording where someone said something useful and you want the bit between minutes 14 and 19 as a voice memo. Maybe it's a screen capture where you want the audio for a podcast. Maybe you saved a video off Instagram and only the music matters.
The technical name for this is "demuxing" — separating the audio track from the container without re-encoding. The audio is already inside the file as MP3 or AAC; you just need to pull it out.
The annoying part of doing this online
Search "MP4 to MP3" and you get a wall of sites that all do the same thing: upload your video, wait, download an MP3. There are a few problems with that flow:
- Your video uploads to a stranger's server and sits there for some retention window.
- A 500 MB video takes minutes to upload and minutes to download — for a job that, locally, takes seconds.
- The free tier usually caps at 100 MB or 5 minutes; past that, paywall.
- Half the sites have aggressive ads and pop-up windows that beg for browser permissions.
Browser-side
Buncha's Audio Extractor does the same job locally. Drop a video file (MP4, MOV, WebM, MKV — any container your browser can read), and it pulls the audio track out as an MP3 or WAV. Nothing uploads.
The conversion uses ffmpeg.wasm — a WebAssembly build of ffmpeg that runs entirely in your browser. The first time you load the tool it downloads about 25 MB of WASM (cached after); after that, extraction is roughly real-time, often faster — a 30-minute video processes in well under a minute.
MP3 vs. WAV — which to pick
- MP3: smaller file, perfect for sharing, the format every player understands. Use this unless you have a reason not to.
- WAV: lossless, large, good if you're going to edit the audio further (importing into Audacity, GarageBand, or a DAW).
If you're saving for a podcast platform, MP3 at 128–192 kbps is the right answer. WAV is for the editing intermediate.
What about MOV files?
iPhones record video as MOV with the audio in AAC. The same tool handles them — drop a .mov in, pick MP3 as the output, download. The QuickTime container is supported as long as your browser can decode it (every modern browser can).
The "I just want this one bit" problem
If you only want a slice of the audio (start at 2:13, end at 2:47), you've got two options:
- Extract the full audio first, then trim it in the Audio Trimmer — drag two handles to set the in/out points.
- Or use the Video Trimmer to crop the video first, then extract the audio.
For one or two clips, option 1 is faster.
Why not just install ffmpeg?
Installing ffmpeg locally is the right answer if you're doing this every day. It's free, fast, and scriptable:
ffmpeg -i input.mp4 -vn -ab 192k output.mp3
But for the once-or-twice-a-month case — a Zoom recording, a screen capture, a downloaded video — the install + remember-the-syntax overhead isn't worth it. Browser-side is one drop and one click.
Privacy of voice notes
This is worth flagging: the most common reason people extract audio from a video is a meeting recording with private content. Sending that to a server-side converter means your colleagues' voices, names, and whatever was said are now on a third party's infrastructure. Browser-side conversion has none of that exposure — the file never leaves your device.
The shortest path
Open the extractor, drop the video in, pick MP3, download. If you only want a slice, open the trimmer afterwards and drag the handles. Both are browser-only and free.