What is an Opus file?
Opus is a lossy audio codec standardised by the IETF as RFC 6716 in 2012. It grew out of work by Xiph.Org and Skype, and it was built for the internet: low delay, good at speech and good at music. It covers bitrates from 6 kbps up to 510 kbps and always runs at 48 kHz internally.
You meet Opus more often than you might think. WhatsApp voice notes, Discord voice, most WebRTC video calls and many browser recordings use it. Files usually end in .opus or .ogg, and a WhatsApp voice note may arrive as .opus or with an .ogg extension. Either way the audio is the same codec in an OGG container.
Why change Opus to MP3
Opus is technically excellent, but support is uneven outside browsers and Android. Windows Media Player, older iPhones and Macs, many car systems, email previews and a lot of editing apps will not play it. MP3, standardised in 1993 and patent-free since 2017, plays nearly everywhere.
So the usual reason to convert Opus to MP3 is simple: you want to send, archive or edit a recording and you do not want the other person, or the other app, to hit an "unsupported format" error.
Opus vs MP3
Opus is far more efficient, which is why a small Opus file needs a bigger MP3 to sound the same.
| Feature | Opus | MP3 |
|---|---|---|
| Released | 2012, IETF RFC 6716 | 1993, MPEG-1 Audio Layer III |
| Compression | Lossy | Lossy |
| Bitrate range | 6 to 510 kbps | 32 to 320 kbps |
| Voice note size per minute | ≈ 0.12 to 0.24 MB at 16 to 32 kbps | ≈ 0.96 MB at 128 kbps |
| Music size per minute | ≈ 0.96 MB at 128 kbps | ≈ 1.44 MB at 192 kbps |
| Compatibility | Browsers, Android, VLC | Almost universal |
| Best for | Calls, voice chat, streaming | Sharing and playback anywhere |
Choosing a bitrate for Opus to MP3
This is where Opus differs from other sources. Because Opus squeezes so much into a low bitrate, the MP3 will be larger than the Opus file. That is normal and does not mean anything went wrong.
- Voice notes and calls: 128 kbps MP3. The Opus source is usually 16 to 32 kbps speech, and nothing is gained going higher.
- Podcasts and talk recorded in Opus: 128 or 192 kbps.
- Music in Opus at 96 to 160 kbps: 192 or 256 kbps MP3, since MP3 needs more bits to match Opus.
- Anything you will edit further: 320 kbps, or convert to WAV instead.
What happens to quality
Opus to MP3 is lossy to lossy. The Opus is decoded, then encoded as MP3 by a LAME-based encoder. The MP3 cannot be better than the Opus. It can only be very close to it or a bit worse. Choosing a generous bitrate from the list above keeps the extra loss out of earshot.
Opus decodes at 48 kHz, and the MP3 keeps that sample rate. If you need 44.1 kHz for a CD project, convert to WAV first and resample in your editor.
Opus to MP3 on iPhone, Android, Mac and Windows
The converter is a web page, so it works the same way on every system. On iPhone, save the voice note to Files first, then open AudioDrop in Safari and pick it. On Android, Chrome can open files from Downloads or from the folder your chat app saves media to. On Mac or Windows, drag .opus files from Finder or Explorer into Chrome, Edge, Safari or Firefox.
If a file has an .ogg extension but came from a voice chat app, it is almost certainly Opus. Drop it in anyway. AudioDrop reads the audio inside, not just the name.
Your voice notes stay on your phone
Voice messages are about as private as audio gets. AudioDrop never uploads them. The Opus to MP3 conversion runs in your browser using WebCodecs for decoding and WebAssembly for the MP3 encoder, on your own device.
It is free, with no account and no watermark. After the page loads it works offline. There is no fixed file size cap, just your device's memory. Drop a batch of voice notes and they convert in parallel, each with its own download. Tags and chat metadata may not carry over.