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Opus to MP3
Convert Opus to MP3 Online — WhatsApp Voice Notes Included
Turn .opus voice messages and audio files into MP3s that play anywhere.
Nothing is enforced, but the file is decoded to 32-bit float in this tab — a voice note at 24 kbps expands more than fiftyfold, which is nothing at voice-note length and real over an hour of recording.
About Opus to MP3
If you have a file ending in .opus, it is almost certainly a voice message. WhatsApp, Signal and Telegram all record voice notes as Opus in an Ogg container, and exporting a chat or saving a message hands you exactly that. Opus is an excellent codec — it was designed for real-time speech and it is genuinely better than MP3 at the low bitrates voice notes use — but almost nothing outside a browser or a messaging app will play the file. Windows Media Player, older iPhones, car stereos, transcription services, video editors and most upload forms all want MP3. This tool decodes the Opus stream and encodes an MP3 from it, which makes the file openable everywhere at the cost of a second generation of lossy compression. For speech that cost is small and 128 kbps is plenty; there is nothing to gain from 320 kbps when the source was recorded at 24. Expect the MP3 to be considerably larger than the Opus file even so, because MP3 is far less efficient at speech bitrates — a one-minute voice note that took 200 KB as Opus can land near 1 MB as a 128 kbps MP3. That is the price of a format everything opens. The decode runs through the browser where it can, through an FFmpeg engine served from this site where it cannot, and the recording never leaves your device.
Questions
Can I convert WhatsApp voice notes with this?
Yes — that is the main reason this page exists. WhatsApp, Signal and Telegram all record voice messages as Opus in an Ogg container, which is what the .opus extension means. Export the message or save the attachment, drop it here, and you get an MP3 that plays in anything.
Why is the MP3 bigger than the Opus file?
Because MP3 is far less efficient at speech bitrates. Opus was designed for exactly this job and a voice note is often recorded around 24 kbps; MP3 needs several times that to sound comparable. A one-minute note that took 200 KB as Opus can land near 1 MB as a 128 kbps MP3. That is the cost of a format everything opens.
What bitrate should I use for a voice message?
128 kbps is more than enough, and often generous. The source was compressed heavily for a phone network, so encoding at 320 kbps produces a much larger file that carries no more detail — a higher bitrate cannot recover what Opus already discarded.
Does the conversion lose quality?
Yes, but not much that you will hear on speech. Opus is lossy and MP3 is lossy, so this is a second generation of compression. For music that matters and a high bitrate is worth it; for a voice note the source is already the limiting factor and the re-encode is barely the weak link.
Why does the waveform sometimes fail to draw?
The waveform preview only uses the browser's own decoder, deliberately — drawing decoration is not worth a 31 MB download. In a browser that cannot decode Opus, mainly Safari, the preview gives up and the canvas says so, while the conversion carries on through the FFmpeg engine and produces the same MP3.
Is my file uploaded to a server?
No. Transmute processes everything locally in your browser using JavaScript and WebAssembly. Your files never leave your device — there is no server, no upload, no cloud processing.