Opus (IETF Open Audio Codec)

Opus — the open-source IETF-standardized successor to both MP3 and AAC, optimized for streaming-friendly variable bitrate and ultra-low latency. Audibly transparent at 128 kbps stereo (better than AAC at equivalent rates); the dominant codec for WebRTC-based voice and increasingly for streaming music.

Used by Spotify (alongside Ogg Vorbis), YouTube Music (alongside AAC), and most modern open-source streaming stacks. Not yet a consumer-facing brand the way ‘MP3’ or ‘FLAC’ are.

For higher bitrates and audiophile use the lossless containers (FLAC, ALAC) are appropriate.