Upload a Opus file and get a M4A back. No signup, no watermark, no limit on how many.
Opus is the best lossy codec in general use: at 64 kbps it beats formats running at twice that, which is why real-time applications standardised on it.
Where you run into it: WhatsApp and Telegram voice notes, Discord, Signal, Zoom, and most browser-based calls.
What it costs you: Everything can play it inside an app and remarkably little can play it as a file — a voice note saved to a desktop is the classic case, and the usual reason to convert one.
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: Opus 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. Opus 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.
Not here. Opus can be read but not written by this converter — ffmpeg decodes it happily, and encoding back to it would mean a format almost nothing plays. If you need the original Opus, keep it rather than recreating it.
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.