MP4 to MP3

MP3 quality is measured in kilobits per second (kbps): more bits keep more detail and make larger files. Each minute of sound takes about 0.9 MB at 128 kbps, 1.4 MB at 192 kbps and 2.3 MB at 320 kbps. The converter shows the expected size for your file before you start.

Most videos from phones, cameras and the web store their sound as AAC. Choosing M4A copies that AAC sound into an audio file exactly as it is: the conversion is very fast and there is no loss of quality at all. M4A plays on iPhones, Android phones, Windows, Macs and in every modern browser and music app.

MP3 is the most widely supported audio format of all, including older car stereos, MP3 players and some editing software, but it means encoding the sound again, which loses a little detail. At 192 or 320 kbps the difference is very hard to hear. If the video's sound is not AAC (WebM videos use Opus, for example), M4A converts it to AAC at 192 kbps.

When you open a single file, a player appears with Start and End fields. Play the video, pause at the moment you want, and press Use current position next to Start or End; or type a time as seconds (75) or minutes and seconds (1:15, or 1:15.5 for half a second). The selected length is shown below, and the size estimate follows it. When you drop several files, each one is converted in full.

Online converters usually upload your video to a server, which is slow for large files and means a copy of your recording leaves your hands. Here the file is read in pieces directly from your device and processed by your browser's built-in media decoder (WebCodecs), so even long videos start converting immediately and nothing is sent anywhere. Files up to 2 GB can be opened.

The converter works in current versions of Chrome, Edge, Firefox and Safari on computers and phones. Each file is checked by its content, not its name, so a picture renamed to .mp4 is refused with a clear message. Some iPhone videos use H.265 (HEVC); their sound can still be extracted, because only the sound track is decoded.