Convert WebM to MP3
Turn WebM video or audio into MP3 for players and car stereos that refuse WebM. Batch convert any number of files locally, with nothing uploaded.
- Runs in your browser
- Files are never uploaded
- Free, no account
First use downloads the 10 MB video engine from this site. After that it is cached and works offline. It is WebAssembly served from onthisdevice.com — no third-party CDN — and your file is still processed entirely on your own device.
Opus in, MP3 out
Nearly every WebM file carries its audio as Opus, a codec that is genuinely better than MP3 at every bitrate — noticeably so below 96 kbps, where MP3 starts to sound watery and Opus still sounds like speech. Converting Opus to MP3 is therefore a step down in efficiency, and you should only do it for a reason: a car stereo, an old hardware player, a piece of transcription software, a DAW that will not import WebM, a client who asked for MP3.
Because it is a step down, give it room. 192 kbps or higher keeps the second compression out of earshot on music; for pure speech, 128 kbps mono is more than enough and halves the file.
Where WebM audio comes from
| Source | File | Typical audio |
|---|---|---|
| Browser voice recorders and web apps | .webm or .weba | Opus, mono, 48 kHz |
| Browser and tab screen recordings | .webm | Opus, stereo |
| Saved web video | .webm | Opus at 128-160 kbps |
| Meeting and call recorders | .webm | Opus, often mono at a low bitrate |
| Telegram voice messages | .ogg or .webm | Opus, mono |
.weba files work too
A .weba file is a WebM container with only an audio stream in it — the extension
browsers use when a recording never had a camera attached. It is handled identically here;
there is simply no video track to throw away, so it converts almost instantly.
Voice notes and transcription
This is the most common reason people land on this page. A web app recorded an interview, a standup or a lecture, and the transcription service, the note app or the person you are sending it to wants MP3. For that job:
- Choose 128 kbps and tick downmix to mono. Speech recognition gains nothing from stereo or from a higher bitrate.
- An hour of audio comes out around 55 MB, which fits comfortably in an email.
- Nothing is uploaded during the conversion, which matters when the recording is a client call, a medical appointment, an HR meeting or a legal interview. Whatever is in that file stays in this tab.
Batch conversion, no counter
Queue as many recordings as you like; they run one after another and can be downloaded as a single ZIP. Upload-based converters meter this operation because each file costs them bandwidth twice over. Locally, the twentieth file costs the same as the first: nothing.
If you wanted the video too
WebM to MP4 converts the whole file, picture included — useful when the recording needs to go into an editor or onto an iPhone. If the file is a browser screen recording that will not scrub, that page also explains why, and fixes it.
Questions
What is inside a WebM audio track?
Almost always Opus, occasionally Vorbis. Opus is technically better than MP3 at every bitrate, so converting is a step down in efficiency — you do it for compatibility, not for quality. Use 192 kbps or higher so the second compression stays inaudible.
Will this work on a .weba file?
Yes. A .weba file is a WebM container with only an audio stream, and it is handled exactly the same way — the tool simply has no video to discard.
Can I convert a browser voice recording?
Yes, that is the common case. Voice notes captured by a web app are usually WebM/Opus, and many transcription services, DAWs and phones want MP3 or WAV instead. Mono at 96-128 kbps is plenty for speech and halves the file.
Does the length of the file matter?
Only for time. There is no duration cap here, unlike the 100 MB or 10-minute limits most upload converters enforce to protect their servers. A two-hour recording works; it just takes proportionally longer.