399 Opus 251 New — Codecs Av01008m08

The identifiers represent specific internal format codes (itags) used by YouTube to deliver video and audio streams via the Google YouTube Video API

8) Debugging & interoperability

• Encoding complexity – AV1 is still 5–10× slower than H.264 for real-time use.
• Opus 251 licensing – While Opus is royalty-free, some patent pools claim AV1 overlaps with HEVC.

• 251 is the WebM-in-DASH codec identifier for Opus (see WebM DASH spec).
• Opus is a standard codec – confirmed safe.

1. Normalize to standard RFC 6381 codec strings – e.g., av01.0.08M.08, opus.
2. Remove non-standard tokens (399, new) – put them in separate attributes.
3. Test with real devices – opus support is universal except old iOS.

• Speech: 12–32 kbps mono
• General voice/music: 32–64 kbps mono, 64–128 kbps stereo
• High-fidelity music: 128–256 kbps stereo