HDR / wide-gamut metadata carried from SPS VUI through the pipeline
to the MP4 mux colr nclx box. All values default to an SDR
BT.709 baseline so un-annotated StreamInfo constructions stay
backward-compatible.
HDR10 Content Light Level Information per CTA-861.3 / HEVC SEI 144
(content_light_level_info) / AV1 Metadata OBU
METADATA_TYPE_HDR_CLL. Wire-encoded into the MP4 clli box as
2 × u16 BE, total 4 bytes payload.
HDR10 Mastering Display Color Volume per SMPTE ST 2086 / HEVC SEI
message 137 (D.2.28 in the H.265 spec) / AV1 Metadata OBU
METADATA_TYPE_HDR_MDCV. Wire-encoded into the MP4 mdcv box as
8 × u16 BE primaries/white-point + 2 × u32 BE luminance, total 24
bytes payload.
Transfer characteristics per ITU-T H.273 §8.2 / H.265 Table E.4.
Carried on StreamInfo so the MP4 mux’s colr nclx writer can
round-trip HDR10 (ST2084) and HLG content without losing metadata.