Two Codecs in One
Opus merges two technologies: SILK (from Skype), a linear-prediction codec optimised for speech, and CELT, an MDCT codec for music- And it can blend them frame by frame. That lets a single stream switch seamlessly between a talking host and a music bed, which is why it dominates real-time communication: a podcast interview, a game voice channel, and a music stream can all use the same codec at the same time. Opus is also extremely low-latency (as little as 5-26.5 ms), where MP3 and AAC need far longer buffers.
Technical Characteristics
Opus scales from 6 to 510 kbps, always resampling internally to 48 kHz, with frame sizes from 2.5 to 60 ms and full VBR support. Its sweet spot is remarkable: speech is fully intelligible around 16-24 kbps, and music at 96-128 kbps rivals MP3 at 192-256 kbps. Files usually use the .opus extension (Opus in an Ogg container) or ride inside WebM for video. Opus is a mandatory codec for WebRTC, the standard behind browser calls. Metadata uses the same Vorbis comment system as OGG and FLAC, so tags and artwork travel with the file.
When to Use Opus
Opus is ideal for voice recordings, podcast masters at low bitrates, streaming, and any bandwidth-constrained delivery you control. Voice messages exported from WhatsApp or Telegram arrive as .opus/.ogg files, which is the most common reason everyday users encounter the format- Usually followed by discovering their car stereo will not play it. One caution for archivists: Opus is still lossy, so if a recording matters, keep an original lossless copy alongside the small Opus delivery files.
Compatibility
All modern browsers, Android, Windows 10 and later, and Linux play Opus natively. Apple support arrived late and remains partial- Playback works in some contexts, but Apple Music/iTunes will not import .opus files. Hardware players, car head units, and older devices largely lack support, so Opus remains a delivery codec for apps rather than a universal file format.
Converting Opus on mp3.now
To make a voice note or Opus download playable anywhere, the Opus to MP3 converter does it in seconds- 128 kbps is plenty for speech, or use the 128 kbps preset. Going the other way, MP3 to Opus produces very small files for apps and web delivery. You can then merge multiple voice notes into a single MP3 if needed.