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 conversion exists for one reason: an iPhone will not play an .opus file. Inside WhatsApp, Telegram or Signal the audio plays perfectly, because the app decodes it itself — but save that voice note out as a file and hand it to someone on an iOS device and it stops there. The Files app shows it and refuses, Safari will not open it, and there is no setting to change. Encoding the audio as AAC in an MP4 container produces exactly the file iOS does want.
The usual situation is a voice message that has to reach somebody who is on an iPhone, or go into an app that only accepts what Apple accepts. Two practical notes for that. Voice notes are mono, so everything above is halved, and there is no reason to pick a high bitrate for one. And if what you are really trying to do is forward a message rather than archive it, sending it inside the same app it came from avoids this conversion altogether — the wall is only there once the audio becomes a loose file.
Yes, entirely, and there is no cap on how many files you convert. No account, no watermark, no trial.
A little, since both formats are lossy and this is a second encode. Of the four targets here AAC is the closest to Opus in efficiency, which makes it the cheapest second generation available — at Best, a flat 192 kbps, there is far more room than a voice note needs and nothing audible is given up. For a speech recording you can drop to 128 kbps from the list without noticing, and that is usually the sensible choice.
Larger than the .opus, often by a factor of five or more, because a fixed 192 kbps against a 24 kbps source is a deliberate overshoot. A one-minute voice note goes from around 180 KB to something near 1.4 MB. Take 128 kbps if that matters, which for a spoken message is still generous — the point of the overshoot is only to avoid compounding what the first encoder already decided.
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.