OPUS to MP3
Nothing is uploaded. The conversion runs here, on this device.
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What this does
Opus is the codec behind WhatsApp and Telegram voice notes, Discord speech, and most WebRTC calls. It is remarkably efficient — intelligible speech at bitrates where MP3 is unusable — and almost nothing outside a web browser will open the file.
Opus is what WhatsApp and Telegram voice notes are encoded in. It is efficient, and almost nothing outside a browser plays it.
Why the MP3 will be larger than the Opus
A voice note is often encoded somewhere around 16–32 kbps, a range MP3 was never designed for. Converting it produces a bigger file that sounds no better, because the audio has already been through Opus and the MP3 can only carry what came out. That is the trade, and it is worth making when the alternative is a file the recipient cannot play. For a voice note, 64–96 kbps mono is plenty; going higher only grows the file.
Nothing is uploaded
The conversion happens inside this page. Your file is read by the browser, converted here, and saved straight back to your downloads. It is never sent to a server, so there is no upload wait and no size cap beyond what your own device can hold.
Open your browser’s developer tools, switch to the network panel, and convert a file. You will see the converter itself download once, and no upload of your audio at all. That is the whole difference between this and a site that converts on a server, and what that difference actually means is worth a read.
The first conversion is slower
The converter is about 32 MB and downloads the first time you use it, which is the one moment this page is not instant. After that it is cached, and later conversions start immediately, even offline. So do later visits.
Questions
Is this how I open a WhatsApp voice note?
Yes. Exported voice notes are usually .opus or an .ogg wrapping Opus, and both convert here. The audio never leaves your device, which matters more than usual for a private message.
Why is my converted file bigger than the original?
Because Opus is far more efficient at speech bitrates than MP3 is. The size increase is the cost of a format everything can play; the audio itself is not improved by it.
What bitrate should a voice note use?
64 kbps is generous for speech and 96 kbps is more than enough. Anything above that stores the limits of the original recording in greater detail without making it clearer.