Video & audio · 3 min read ·
Extract MP3 from MP4 — right in your browser
Modern browsers can decode and encode media on their own. Here is how in-browser audio extraction works, without uploading the video.
A few years ago, pulling the soundtrack out of a video meant installing desktop software. Today, the browser's built-in media codecs and a small MP3 encoder can do it inside a tab.
The pipeline
The file is read from your disk into the page, the audio track is separated from the video (demuxed), decoded, re-encoded to MP3 and handed back to you as a download. The video itself never leaves your device.
On the desktop, the same job is a single ffmpeg command:
ffmpeg -i input.mp4 -vn -b:a 192k output.mp3Choosing a bitrate
The bitrate decides the size and the quality of the MP3. The 4Dev converter offers 64 to 320 kbps:
320 kbps best quality, about 2.4 MB per minute
192 kbps recommended for music, about 1.4 MB per minute
128 kbps fine for speech and podcasts, about 1 MB per minute
64 kbps voice only, about 0.5 MB per minuteA higher bitrate can’t add quality that isn’t there. Most phone videos store their sound as AAC at about 128 to 256 kbps, so encoding them at 320 kbps makes a bigger file that sounds the same.
For a voice memo, a lecture or a podcast, 64 or 128 kbps keeps the file small and the speech clear. For music you plan to listen to on good headphones, 192 kbps or more is the better choice. If you are not sure, start with 192 kbps: it is the recommended setting and sounds good for both.
MP3 or another format?
- MP3: plays on every device and in every app. The safe default.
- M4A (AAC): smaller than MP3 at the same quality, and native on Apple devices.
- WAV: uncompressed, about 10 MB per minute at CD quality. Useful for editing.
- FLAC: lossless but compressed, usually about half the size of WAV.
- OGG (Opus): excellent quality at low bitrates, but some older devices can’t play it.
Take only the part you need
If you only want a song from a long recording or one answer from an interview, set a start and an end time before converting. The file is smaller, the conversion is faster and you don’t have to cut it again in an audio editor.
Why do it on your own device?
Online converters usually upload the whole video to a server, convert it there and send the result back. For a large file that means waiting for the upload, and your video sits on someone else’s computer, which matters for family videos, meetings and interviews. Converting in the browser skips the upload completely: the time you wait is only the time your own device needs to do the work, and the file never leaves it.
Limits worth knowing
Because the work happens on your device, speed depends on your computer or phone, and very large files need enough memory. The 4Dev video converter accepts files up to 500 MB and also converts MOV, WebM and MKV, trims clips and outputs WAV, M4A, FLAC and OGG.
A word about copyright
Extracting audio from your own videos, or from recordings you have permission to use, is fine. Downloading or redistributing the soundtrack of someone else’s video or music may break copyright rules or a platform’s terms of service, even if a tool makes it technically easy.