Extract audio from video: MP4 to MP3 in your browser
Drop a video on mp3fy’s converter and you get the audio back as an MP3. The video track is discarded, the sound is re-encoded on your own machine, and nothing uploads. A 3 GB lecture never touches the network. That is the entire answer. The rest of this page is the size math, the three steps, and one caveat worth your time.
Why bother? Because video is usually a very heavy wrapper around the part you actually want. A recorded webinar where the slides change four times an hour. A conference talk you will only ever hear on a commute. A three-hour interview that someone, for reasons lost to history, published as a screen recording of a static logo. The picture costs gigabytes. The sound costs megabytes.
The size payoff
Video bitrates swing with codec, resolution and motion, so the middle column below is a range. The MP3 column is plain arithmetic: 192 kbps works out to 1.44 MB per minute, every time, regardless of what the video was doing.
| 1080p video length | Typical video size | MP3 at 192 kbps |
|---|---|---|
| 10 minutes | 170–500 MB | ~14 MB |
| 1 hour | 1–3 GB | ~86 MB |
| 3 hours | 3–9 GB | ~260 MB |
Read the middle row twice. An hour of 1080p is 1–3 GB; the same hour as audio is 86 MB. For anything you were never going to watch, extraction is a 92–97 percent discount. Your phone’s storage, your backup bill and your patience all notice.
The ranges are honest, not hedging. A talking head in front of a whiteboard compresses far better than a handheld concert shot, so two one-hour files can differ by a factor of three. The audio does not care: speech at 192 kbps sounds the same whether the camera sat on a tripod or rode in a jacket pocket.
How to do it
- Open the converter and drop the file on it. A whole folder works too: mp3fy converts everything inside and hands the results back as a ZIP.
- Let it run. Conversion starts immediately with sensible defaults; 192 kbps suits almost everything, and there is a longer argument about bitrates if you enjoy that sort of thing. On current hardware the encode runs at 20–80× realtime, so an hour-long video is done in a minute or three.
- Download the MP3. Title, artist and album tags come along when the source file carries them.
No account, no queue, no watermark stamped into the audio, a real thing some converters do. mp3fy is free and ad-free, full stop.
What converts on your device
MP4, MOV, MKV, WebM, AVI and 3GP are all handled locally. The browser opens the container, decodes the audio track and re-encodes it to MP3 without the bytes going anywhere. Here is how that works if you want the mechanics. Because the file is streamed rather than loaded into memory, there is no size or duration ceiling: a 20 GB screen recording converts the same way a 20 MB clip does, just for longer. The formats page has the full matrix.
What takes the cloud path
Some containers ship with codecs browsers never learned. Old WMV files, ASF wrappers and MTS footage straight off a camcorder fall in this bucket. Those route to mp3fy’s cloud automatically, where native ffmpeg decodes what the browser cannot. Your upload is deleted the moment the MP3 is ready. The privacy page spells out retention, and it is mercifully short reading.
The honest caveat
Extraction re-encodes. The audio inside an MP4 is usually AAC, and AAC to MP3 is a lossy-to-lossy step: one generation of quality is spent in the exchange. At 192 kbps or above you will not hear it on speech, and almost never on music through normal headphones. But almost never is not never. If the recording matters professionally (a session you might master later, an interview a documentary depends on), keep the original video as the archive copy and treat the MP3 as the convenient one. Disk space is cheap; a lost original is not.
For everything else (the lecture, the webinar, the concert filmed on a phone), the MP3 is the version you will actually use. The gigabytes were just packaging.