AV1CodecConfigurationBox (av1C) must match the Sequence Header OBU  #285

The AV1CodecConfigurationBox av1C (defined in AV1 Codec ISO Media File Format Binding § 2.3.2) contains decoder configuration information. This information is also present in the Sequence Header OBU in the AV1 Image Item Data. Since it is advantageous to be able to access this information by parsing the AVIF container without decoding the AV1 Image Item Data, it is duplicated at the container level. Both of these values must match, or else the interpretation of the file would be ambiguous.

This requirement is based on § 2.2.1 of the AVIF Specification.

Since this library currently only handles AVIF container parsing and not AV1 Image Item Data decoding, enforcement of this requirement may occur in the consumer code (see https://bugzilla.mozilla.org/show_bug.cgi?id=1701430).