Codecs: Av01008m08 399 Opus 251 New

The string breaks down into five distinct parts:

| Fragment | Suspected Meaning | Standard Equivalent | |----------|-------------------|----------------------| | codecs | Container metadata field | ISO/IEC 14496-12 (MP4) avcC box equivalent | | av01008m08 | Corrupted AV1 profile string | Likely av01.0.08M.08 or av1 + bitrate | | 399 | Unknown constant | Possibly a bitrate (399 kbps) or a fourCC variant | | opus | Audio codec | IETF RFC 6716 (Opus) | | 251 | Track/program ID | WebM track numbering; YouTube audio format ID | | new | User-added note | Not a codec parameter |

No codec string contains spaces, but users often paste space-separated logs. The actual playing system probably sees: av01.0.08M.08:399:opus:251.

If this string is from your manifest:

Standardized version:

codecs="av01.0.08M.08, opus"

Track ID (399) → id="399"
Flag new → tags or supplementalCodecs in DASH.

The string you've provided represents the peak technical performance of a modern video stream, typically seen in YouTube's "Stats for Nerds". It specifies that you are watching a video using the most efficient video codec currently available (AV1) paired with the highest quality standard audio stream (Opus 251). Feature: The "Perfect" Stream Signature codecs av01008m08 399 opus 251 new

When these specific identifiers appear together, it indicates a high-end playback experience optimized for both visual clarity and data efficiency:

opus 251 · TeamNewPipe NewPipe · Discussion #10762 - GitHub

Use MediaCapabilities API:

const videoConfig = 
  type: 'file',
  video: 
    contentType: 'video/mp4; codecs="av01008m08"',
    width: 1920,
    height: 1080,
    bitrate: 2000000,
    framerate: 30
  ,
  audio: 
    contentType: 'audio/webm; codecs="opus"'
;
navigator.mediaCapabilities.decodingInfo(videoConfig).then(result => 
console.log('Supported:', result.supported);
console.log('Smooth:', result.smooth);
);