Opus is an open, royalty-free codec (RFC 6716) that became the universal default for real-time audio and the mandatory codec in every WebRTC stack. Its trick is hybridizing two engines: a SILK speech layer from Skype and a CELT music layer, switching or blending between them per frame. That lets one codec span 6 kbps voice to 510 kbps full-band stereo, with frame sizes from 2.5 to 60 ms, so it tunes for either ultra-low latency or efficiency. Built-in in-band FEC and DTX make it resilient on lossy networks. Outside calls, Opus is also strong for streaming and podcasts where hardware support isn't required.
