Parse the DTS core header (SFREQ/AMODE/RATE/LFF/NBLKS/FSIZE) → a ddts box
(sample rate, channel layout mask, core size, computed bitrate, LFE);
whole access units (core + DTS-HD extension substreams) pass through, so
an HD decoder finds the extension. dtsh when an extension sync follows the
core, else dtsc. Fit oracle now carries DTS / DTS-HD MA / DTS-HD HR.
Validated on 300 (real DTS-HD MA 7.1): freemkv's mp4 DTS track is
byte-identical to ffmpeg -c copy under ffprobe (dts / 48000 / 8ch / 7.1)
and decodes clean (exit 0). Channel layout correct.
moov now precedes mdat. At create() reserve a moov-sized hole (a free
box) between ftyp and mdat: reserve = round_up_4MB(16 B/sample ×
est_samples) + 4MB buffer, floored at 8MB. Because the hole precedes
mdat, sample offsets are fixed from the start — no rewrite, no offset
patch. finish() writes moov into the hole and pads the slack with a free
box; if the estimate is blown it falls back to moov-at-end. Streams over
HTTP without a pre-fetch. Reserve-math + box-order tests added.
Read side of mp4://: parse moov/trak/stbl (stsd codecs+hvcC/avcC/channel
info, stsz/stco/co64+stsc → per-sample offsets, stts+ctts → decode/
composition timing, stss → sync), rebuild a DiscTitle, and emit samples
as PesFrames in global decode order. Video NALs are length-prefixed in
MP4 — the exact framing the MKV muxer wants — so no reframing. Wired into
input() so mp4:// flows to every sink (mkv://, audio://, json://, …).
In-memory write→read round-trip test proves symmetry (streams, hvcC,
sample sizes survive). Progressive MP4 only; fragmented (moof) is future.
Make Mp4Sink generic over a seekable writer; the CLI output() arm wraps
the file in WritebackFile (as mkv:// does) so a UHD-scale mux to slow /
NFS staging avoids the dirty-page burst. The mdat backpatch is an
ordinary seek WritebackFile already handles (seek_then_patch_roundtrip).
Tests switched to in-memory Cursor writers.
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