What is Opus (audio codec)?
Definition
Opus is a modern, open, royalty-free lossy audio codec that works from low-bitrate speech to high-quality music. It usually beats MP3 and AAC at low bitrates and is the standard audio codec in WebM, used by YouTube and many chat apps.
Opus is a lossy audio codec, meaning it shrinks audio by discarding sound that is hard to hear and reconstructing a close approximation on playback. What makes it unusual is its range: one codec handles low-bitrate voice calls and high-fidelity stereo music well. It does this by combining two earlier technologies, SILK for speech and CELT for music, and switching or blending between them as needed.
Opus matters because it is open and royalty-free, so anyone can use it without licensing fees, and it delivers strong quality per bit. At low bitrates it typically sounds clearer than MP3 or AAC, which is why it powers VoIP and chat apps like Discord, plus the audio track in WebM video. YouTube serves much of its audio as Opus.
A common confusion is the container versus the codec. Opus is the encoded sound, while Ogg and WebM are the files (containers) that hold it; a .opus file is usually an Ogg container. Opus is not the same as MP3 or AAC, and unlike lossless formats such as FLAC, it does not perfectly preserve the original audio.
Quick facts
- Open, royalty-free lossy audio codec standardized by the IETF (RFC 6716)
- Combines SILK (speech) and CELT (music) for a wide bitrate range
- Usually outperforms MP3 and AAC at low bitrates
- Standard audio codec in WebM; used by YouTube, Discord, and other apps
- Typically stored in Ogg (.opus) or WebM containers