Upload a MP3 file and get a M4A back. No signup, no watermark, no limit on how many.
MP3 is the format that made portable music work, and thirty years on it is still the one every device, car stereo, DAW and browser will open without being asked twice.
Where you run into it: Downloads, podcast feeds, old music libraries, anything a client sends you and expects you to just play.
What it costs you: It throws audio away to get small, and at 320 kbps almost nobody can hear what went. What matters is that the discarded part never comes back.
M4A is an MPEG-4 container holding AAC audio — the same codec as a bare .aac file, wrapped so that players, tags and cover art all behave.
Where you run into it: iTunes and Apple Music purchases, voice memos, Zoom and Teams recordings, most phone-recorded audio.
What it costs you: Outside Apple's ecosystem support is good but not universal, and a few older tools still refuse the extension on sight.
This is a transcode between two lossy formats, so it is a second generation: MP3 already discarded detail to get small, and M4A now encodes what is left and discards a little more. On a 320 kbps source you are unlikely to hear it. On something already thin — a voice note, a 96 kbps download — you may. Convert from the best copy you have, never from a copy of a copy.
Yes, entirely, and there is no cap on how many files you convert. No account, no watermark, no trial.
A little, in principle. MP3 is already a lossy format and M4A is another one, so the audio is encoded a second time and a small amount more is discarded. From a good source it is very hard to hear; from an already-thin file it can be audible. Always convert from the best copy you have.
Roughly comparable, depending on the quality you pick. At the same bitrate the two files land within a few percent of each other; drop the bitrate and the M4A gets proportionally smaller.
Yes — M4A is one of the formats this converter writes, so the reverse page exists at /m4a-to-mp3/. Remember that going back and forth between two lossy formats degrades the audio a little each time.
The file is uploaded to do the conversion — nothing here runs in your browser — and both your upload and the converted result are deleted the moment the file is sent back. Nothing is stored and nothing is logged beyond the request itself.