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mux/mkv: spec-conformance fixes (field order, CICP, VobSub idx, SeekHead, AC-3)

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- FieldOrder now derives from the bitstream's measured top_field_first
  (Some(true)→TFF, Some(false)→BFF) instead of hardcoding TFF for all
  interlaced content; falls back to TFF when unmeasured. Adds
  VideoStream::top_field_first; DVD/BD scan sets None with a precise
  TODO(spec) for parser→title plumbing.
- CICP (matrix/transfer/primaries/range) now prefers measured CICP from
  the bitstream (VideoStream::measured_cicp) over the coarse ColorSpace
  enum, so the container stops assuming a colour space the stream may
  contradict. Enum remains the fallback.
- VobSub S_VOBSUB CodecPrivate now emits a `size: WxH` line ahead of the
  palette per the .idx format so players place/scale subs correctly.
- SeekHead: when zero cues are written, the CUES Seek entry is Voided
  instead of leaving a dangling pointer to the Cues offset (now Tags/EOF).
- AC-3 Channels back-patch offset is captured from the writer instead of
  the hardcoded chan_elem_pos+2 (decoupled from the VINT width choice).
- Hoisted inline CICP codes and the dvcC fourcc to named constants citing
  ITU-T H.273 / RFC 9559; fixed the stale FieldOrder comment.
- DefaultDuration vs pulldown: precise TODO(spec) left (needs the same
  parser→title channel as top_field_first).

Tests: BFF-from-measured-flag, measured-CICP-overrides-enum, VobSub size:
line present/omitted, zero-cue SeekHead Void. precommit (1.86) green.
This commit is contained in:
Matthew Jackson
2026-06-25 18:40:30 -07:00
parent 8e0797eab0
commit 43fb97f71f
17 changed files with 514 additions and 54 deletions
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src/mux/ebml.rs
+10 -9
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@@ -394,6 +394,10 @@ pub const SEGMENT: u32 = 0x1853_8067;
// SeekHead
pub const SEEK_HEAD: u32 = 0x114D_9B74;
pub const SEEK: u32 = 0x4DBB;
/// Void — RFC 9559 (Matroska) §EBML global element 0xEC. Used to neutralise a
/// reserved-but-unused region (e.g. the CUES SeekHead entry when no Cues element
/// is written) so it carries no meaning to a parser.
pub const VOID: u32 = 0xEC;
pub const SEEK_ID: u32 = 0x53AB;
pub const SEEK_POSITION: u32 = 0x53AC;
@@ -436,16 +440,13 @@ pub const FIELD_ORDER: u32 = 0x9D;
pub const INTERLACED_INTERLACED: u64 = 1;
pub const INTERLACED_PROGRESSIVE: u64 = 2;
// FieldOrder values (Matroska / RFC 9559, element 0x9D): 1 = top-field-first,
// 6 = bottom-field-first, 2 = undetermined, 0 = progressive. NTSC DVD (480i),
// PAL DVD (576i) and HD (1080i) are all emitted top-field-first — the muxer
// hardcodes TFF for every interlaced DVD/HD source (DV is the only common BFF
// source and freemkv does not produce it). 0xFF is our sentinel for
// "undetermined / omit".
// 6 = bottom-field-first, 0 = progressive. The muxer derives TFF vs BFF from the
// bitstream's measured top_field_first when available, falling back to TFF for
// interlaced content (NTSC 480i / PAL 576i / HD 1080i are overwhelmingly TFF).
// 0xFF is our sentinel for "undetermined / omit the element".
pub const FIELD_ORDER_TFF: u8 = 1;
// Bottom-field-first. Retained for completeness/round-trip tests; the muxer
// emits TFF for all DVD/HD interlaced content (DV is the only common BFF
// source and freemkv does not produce it).
#[allow(dead_code)]
/// Bottom-field-first (RFC 9559 element 0x9D = 6). Emitted when the bitstream's
/// measured top_field_first is false.
pub const FIELD_ORDER_BFF: u8 = 6;
pub const FIELD_ORDER_UNDETERMINED: u8 = 0xFF;
pub const DISPLAY_WIDTH: u32 = 0x54B0;