Read an AV1 codec string without dropping field widths

The useful distinctions

• The AV1 codec string begins with av01.
• Its required fields include profile, level, tier, and bit depth.
• The level field encodes a level index rather than a decimal display level.

Preserve the structured spelling

The synthetic AV1 identifier contains required fields only. Copy it exactly before interpreting the positions: the profile field is zero, the level-and-tier field is 04M, and the bit-depth field is 08. The leading zeroes are part of the defined spelling, so a generic number formatter should not remove them while producing a report. Treat the tier letter as part of its own structured field rather than a suffix on an arbitrary number.

Distinguish parsing from support

Turning the identifier into a field ledger helps a developer compare it with an implementation's documented limits. It does not establish that a browser accepts the combination or that a particular file's samples match it. Optional colour and chroma details have their own rules, and a short identifier should not be expanded by guessing values from the article's title. If an authoring pipeline supplies longer strings, check whether the optional group is complete and consistent with the actual configuration. The example demonstrates the required-field grammar only, using an invented combination that is syntactically permitted by the binding specification read. The level field's leading zero is part of the declared grammar, so preserve 04 during serialization. Converting it to a free-form label and writing that label back would change the codec string.

Worked example · synthetic

The string declares profile 0, level index 04, Main tier, and 8-bit depth. The level index corresponds to level 3.0 in the AV1 level numbering; no decoder has been queried.

Synthetic text example; no network operation has been performed.

video/mp4; codecs="av01.0.04M.08" 

Check the interpretation

• Keep required field widths.
• Distinguish a level index from its human-readable level.
• Verify configuration and optional fields against actual media.