oa::VideoDemuxer::Av1Config

codec config parsed from av1C (AV1 ISO-BMFF §2.3): the configOBUs blob, which carries the sequence-header OBU out-of-band. AV1 MP4 samples are OBU temporal units that omit the sequence header, so we prepend this to every keyframe temporal unit (analogous to SPS/PPS for H.264/H.265).