Аудио
Перекодируем M4A, AAC и другие звуковые файлы в MP3 с выбором битрейта. Декодирование и кодирование идут в браузере, файл не уходит на сервер.
M4A и MP3 — оба формата с потерями, поэтому перекодирование немного ухудшает звук. Для музыки берите 192 kbps и выше, для речи и подкастов хватит 96–128 kbps.
Tool guide
M4A is a container holding AAC audio, the default output of the iPhone voice recorder, Apple Music and many messengers. The file itself is fine, but older car stereos, some audio players and certain podcast upload forms accept only MP3. This tool decodes the audio with the browser's own decoder and encodes MP3 using the LAME encoder compiled to JavaScript. Nothing is uploaded, so personal recordings and work interviews can pass through safely. See also: pack a WAV back into M4A, rip the sound out of a video file as MP3, squeeze an uncompressed WAV down to MP3.
Slightly, and it is unavoidable: both formats are lossy, so this is a re-encode rather than a repackage. The difference is normally inaudible if you keep the bitrate at or above the source — for AAC at 256 kbps choose MP3 at 192-256 kbps. Lower it only deliberately, to save space.
192 kbps is a sensible floor for music; 256 and 320 kbps are worth it for good headphones. Speech, lectures and podcasts are fine at 96-128 kbps, and with the mono option the file becomes a quarter the size of stereo 192 kbps at the same intelligibility.
It is not. The audio is decoded by the browser's built-in decoder and encoded by the LAME library loaded onto the page as an ordinary script. No network request carries the file contents, which you can confirm in the Network tab of developer tools.
MP3 encoding is real computation and your CPU does it, not a server. Throughput is roughly 10-30 times faster than real time, so an hour of audio takes two to three minutes. Keep the tab open while it runs.
Anything the browser itself can decode: M4A, AAC, MP4, WAV, OGG, WebM and usually FLAC. Formats browsers do not support — WMA, APE, older AMR variants — need to be converted to one of these first.
There is no hard limit, but the decoded audio is held in the tab's memory while it works. An hour of stereo occupies roughly 600 MB uncompressed, which can crash a tab on a weak laptop or a phone. Split long recordings or use the mono option.
Before: interview.m4a, 40 minutes, stereo
After: interview.mp3 at 96 kbps mono — about 27 MB instead of 75
Before: track.m4a, AAC 256 kbps
After: track.mp3 at 256 kbps — plays on factory head units and old players
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