Convert MP3 to Opus for smaller files at the same quality
This MP3 to Opus converter re-encodes MP3 files with Opus, the open, royalty-free codec standardised by the IETF in 2012. Opus is remarkably efficient: speech is clear at 24–32 kbps and music is very hard to tell from the source at 96–128 kbps, so an audiobook, lecture or podcast archive can shrink to a third of its MP3 size or less.
The files are standard Ogg Opus (.opus), encoded by your browser’s built-in WebCodecs Opus encoder, with tags and cover art kept as comment fields. Nothing is uploaded. As with any lossy-to-lossy conversion, the Opus file can only sound as good as the MP3 it came from — the win here is size, not quality.
How to use the MP3 to Opus Converter
- Drop the MP3 episodes, lectures or songs you want to shrink onto the upload area.
- Pick a Bitrate: 128 kbps (selected) for music, 64–96 kbps for podcasts, 32–48 kbps for speech-only recordings.
- Set Channels to Mono for voice — Opus then spends every bit on the single channel. The sample rate is fixed at 48 kHz, the rate Opus always uses.
- Press Convert to Opus and watch the progress.
- Download the .opus files one by one, or all together as a ZIP.
MP3 to Opus Converter features
Browser-native Opus encoder
The WebCodecs Opus encoder built into Chrome, Edge and Firefox (libopus) at 32–256 kbps, stereo or mono.
Standard .opus files
Ogg Opus as defined in RFC 7845, playable in browsers, VLC, Android, foobar2000 and most modern players.
Tags and cover art
ID3 tags become Opus comment fields, and the cover image is embedded as METADATA_BLOCK_PICTURE.
Size estimate up front
Each file shows the expected Opus size before you convert, worked out from the bitrate and length.
Batch and ZIP
Convert an entire podcast back catalogue in one go.
Opus bitrate guide
For comparison, an hour of 128 kbps MP3 is also about 55 MB; the same spoken-word podcast as 48 kbps mono Opus is about 21 MB.
| Bitrate | Size per hour | Good for |
|---|---|---|
| 32 kbps mono | ≈ 14 MB | Speech: audiobooks, lectures, voice notes |
| 64 kbps | ≈ 27 MB | Podcasts with music beds, radio shows |
| 96 kbps | ≈ 41 MB | Music for phones and streaming |
| 128 kbps | ≈ 55 MB | Music from good MP3s |
| 192–256 kbps | ≈ 82–110 MB | Archival copies of 320 kbps MP3s |
Where .opus files play
- Chrome, Edge, Firefox and other modern browsers play Opus in an audio element, which makes it a good format for web audio.
- Android, VLC, foobar2000, mpv and Kodi open .opus files directly.
- Support on older Apple software, car stereos and some editing programs is patchy — keep MP3 or M4A copies for those, or convert back with Opus to MP3.
How the conversion works
Your browser decodes the MP3 with its own decoder. Mediabunny (MPL-2.0) then resamples the audio to 48 kHz — Opus’s working rate — mixes it to mono if you asked for that, and feeds it to the browser’s WebCodecs Opus encoder. The encoded packets are written into Ogg pages with an OpusHead and an OpusTags header carrying your tags and cover art. No step leaves your device, and nothing is stored once you close the tab.
Opus, AAC or Vorbis?
All three are modern lossy codecs. Opus is the most efficient at low and medium bitrates and the best for speech; AAC (MP3 to AAC) is the safest choice for Apple devices; Vorbis (MP3 to OGG) is what many game engines expect. Starting from an MP3, none of them can improve the sound, so pick the one your players support and a bitrate that keeps up with the source.
MP3 to Opus Converter FAQ
How do I convert MP3 to Opus?
Drop the MP3 files here, choose a bitrate (128 kbps for music, 32–64 kbps for speech) and press Convert to Opus.
Is Opus better than MP3?
At the same bitrate Opus sounds clearly better, especially below 128 kbps. Converting an MP3 doesn’t add quality, but it can make the file much smaller with little audible loss.
Why is Opus always 48 kHz?
Opus works internally at 48 kHz. Players resample automatically, so a 44.1 kHz MP3 converts without any problem.
Will my phone play .opus files?
Android phones play them natively. On iPhone, support depends on the app, so test one file before converting a whole library.
What bitrate should I use for speech?
32 kbps mono is clear for a single voice; 48–64 kbps gives extra headroom for noisy recordings or music beds.
Does it work privately?
Yes. Once the page has loaded, the conversion runs entirely in your browser with no upload.