Turn the AAC soundtrack of an MP4 into an MP3 at the bitrate you pick, encoded on your own device. Nothing is uploaded, and there’s no account, watermark or limit.
Drop your MP4 files on “Drop MP4 / MOV / WebM / MKV files here”, or tap the area to pick them. Each row shows the duration, the picture size and a note such as “AAC audio encoded to .mp3”.
Under “MP3 quality”, keep “192 kbps (recommended)” or switch to “128 kbps (smaller)” or “320 kbps (best)”.
Press “Convert 1 file to MP3” (the count follows the number of files) and watch each file's percentage.
Save each MP3 with Download, or grab them together with “Download all (.zip)”.
An MP4 is a container: it holds a video track and, almost always, a sound track compressed with AAC. MP3 is a different, older audio codec, so the AAC sound has to be decoded and encoded again. Both formats are lossy, which means the conversion is lossy to lossy: the MP3 cannot be better than the AAC it came from, and a low bitrate adds a second layer of artefacts. At 192 kbps that second layer is inaudible to most listeners, which is why it is the default.
The encoder is LAME, the long-standing open-source MP3 encoder, compiled to WebAssembly and loaded only when you convert. In the rare MP4 whose sound is already MP3, filetidy copies it as is instead of encoding it twice. The video track is simply left out, so the result is a pure audio file.
MP3 size is easy to predict: bitrate in kilobits per second, times the length in seconds, divided by eight, gives kilobytes. A four-minute song at 192 kbps is 192 × 240 ÷ 8 = 5,760 KB, about 5.8 MB; at 320 kbps the same song is about 9.6 MB.
The MP3 keeps the source's sample rate and is stereo at most. Title, artist and cover art are not written: MP4 metadata is dropped rather than translated into ID3 tags, so add them afterwards in your music app or tag editor if you need them.
Windows
The wrench icon next to the profile opens its settings, where the Audio codec tab sets the MP3 bitrate.
Mac
QuickTime Player's File > Export As > Audio Only saves an AAC file with the .m4a extension, not an MP3. It is fine for Apple devices, but not if you specifically need MP3.
AAC sounds as good as MP3 at a lower bitrate, so if your player handles M4A files there is no quality reason to convert. People pick MP3 for compatibility: older car stereos and USB-stick players, dedicated MP3 players, some DJ software and podcast or radio workflows that expect .mp3, and anything built before AAC became common.
For the bitrate, 128 kbps suits speech, lectures and voice notes where size matters. 192 kbps is the sensible default for music. 320 kbps is the MP3 maximum and only worth it when the MP4's own audio was recorded at a high bitrate; it cannot restore detail the AAC track never had.
If you only want the sound and don't care about the format, extracting the AAC track unchanged into an .m4a is instant and loses nothing. Choose MP3 when a device or app tells you it needs MP3.
Usually not audibly. Phones often record AAC at a moderate bitrate, so a 320 kbps MP3 mostly reproduces the same sound in a file two-thirds larger than at 192 kbps. Pick 320 kbps for music videos or concert recordings you plan to play on good speakers.
No. filetidy drops metadata from every output, so the MP3 has no ID3 tags. The file name is the MP4's name with .mp3 at the end. Music apps such as iTunes, Music or foobar2000, and dedicated tag editors, let you add title, artist and artwork afterwards.
No. Your browser reads the MP4 from your disk, decodes the sound and encodes the MP3 inside a Web Worker on your device. If your browser can't decode the file's audio, a 32 MB compatibility encoder program is downloaded once; your file still never leaves the device.
Multiply the bitrate by the duration and divide by eight. A 10-minute MP4 gives about 9.6 MB at 128 kbps, 14.4 MB at 192 kbps and 24 MB at 320 kbps, whatever the size of the original video, because the picture is discarded.
Yes. Add as many as you like; they are converted one after another to keep memory use low, all at the bitrate you chose. When more than one is finished, “Download all (.zip)” bundles them into a single archive.
Because the AAC sound was compressed once by the camera and is compressed again as MP3. At 128 kbps you may hear swishy cymbals or a duller top end on music. Convert again at 192 or 320 kbps from the original MP4, not from the MP3.
Last updated October 28, 2026