Problem: DPX import rejected the 10/12-bit packed layout (packing 0)
and the Y'CbCr descriptors (100 CbYCrY, 101 CbYACrYA, 102 CbYCr,
103 CbYCrA) with an "unsupported" error.
Fix: unpack packed components back to back, low bits first, each scan
line on a 32-bit boundary (as ffmpeg reads 12-bit packed files), and
convert Y'CbCr to RGB with the matrix the colorimetric field names
(BT.709; BT.601 for the 601 and composite codes; by picture size when
unspecified), in video range unless the reference codes span the full
code range; 4:2:2 chroma is shared by each pixel pair. Unit tests for
every new layout and hostile headers; an ffmpeg oracle test builds
packed 12-bit RGB and 8-bit 4:2:2 / 4:4:4 / 4:4:4:4 files from
ffmpeg's test picture and matches its decode within one 8-bit step.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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