Codecs Av01008m08 399 Opus 251 New May 2026

is currently the king of internet audio. It is a codec so advanced it can switch between speech and music modes in real-time. In the standard YouTube Itag list, 251 specifically refers to Opus audio inside a WebM container, usually at a bitrate around 160 kbps.

| Symptom | Likely Fix | |----------------------------------|----------------------------------------------------------------------------| | av01008m08 unknown in browser | Map to standard codec string ( av01.0.08M.08 ), or serve fallback. | | Opus 251 fails on Safari | Safari requires mp4a – use AAC or remux Opus into MP4 with correct brand.| | new flag ignored | Handle in player logic: prioritize if track label contains "new". | | String malformed (spaces) | Should be comma-separated in standard specs – convert to commas. | codecs av01008m08 399 opus 251 new

These are internal parameters. "0" typically refers to the Main Profile, "08M" indicates the bit depth (8-bit) and level, and the final digits represent specific encoding tiers used by YouTube's servers. is currently the king of internet audio

You are not looking at a codec. You are looking at : | These are internal parameters