Generalize the sink to N tracks: one video + every MP4-mappable audio
track. Audio sample entries built from the first frame's bitstream —
AC-3 (ac-3/dac3) and E-AC-3 (ec-3/dec3), parsing the (E-)AC-3 BSI for
fscod/bsid/bsmod/acmod/lfeon and the data rate. Per-sample audio
durations from PTS deltas (no reorder → no ctts, all sync). Fit oracle
(mp4_fit_report, exported): video HEVC/H264, audio AC-3/E-AC-3;
TrueHD/DTS/LPCM and bitmap subs are excluded with a typed reason so the
CLI can report exclusions — never a silent drop.
Verified vs ffmpeg -c copy on real discs: AVC+AC3 and HEVC(HDR10)+AC3
both frame-exact on every track (video 2650/4270, audio 5567/3454),
duration and colour identical, clean decode. On a pathological 4-clip
title ffmpeg's OWN output emits the same DTS-monotonicity warnings (more
of them) — source-inherent, not a muxer defect.
New mux/mp4: writes ftyp+mdat+moov (moov-at-end), streaming samples into
a 64-bit mdat and building the sample tables in memory, patched at
finish(). Video track (HEVC/AVC): passthrough length-prefixed NALs
(already MP4 framing), full stts/stsz/stsc/co64/stss and signed ctts,
CFR-derived decode timeline (pipeline carries presentation PTS only), and
a colr box for HDR10 colour signalling. hvc1/avc1 sample entry from the
hvcC/avcC codec_private. Fail-loud on codecs with no MP4 mapping.
Verified against ffmpeg -c copy on real discs: AVC-SDR (300) and
HEVC-HDR10 UHD (Dune) both frame-exact (8159 / 8160 frames), colour-exact
(bt2020/smpte2084/bt2020nc), and clean-decoding. Audio + fit oracle land
in M2.
Matthew Jackson