Remove reference-decoder citations from a public MIT-licensed repo
This crate is MIT licensed. Comments citing another decoder's internal symbols and reproducing its tables verbatim create licence risk that no engineering benefit justifies, so every such citation is replaced with the primary source: ETSI TS 102 114 §5.3.1. Eleven sites across src/mux/codec/dts.rs and src/mux/mp4/audio.rs. The technical substance is unchanged in every case — the deficit-sample-count semantics, the reserved-field skips, the invalid LFF value, and the 16 legal AMODE codes are all spec facts and are now attributed as such. Four CHANGELOG entries that named a validator are reworded; the "no a reference decoder" dependency claim stays, since stating what this project does NOT depend on carries no risk. I initially argued this was a false positive on the grounds that the project's hygiene rules name internal infrastructure and reverse-engineering material, not open-source citations, and that a channel-count table from a standard is fact rather than expression. That reasoning missed the point: the exposure is MIT distributing text derived from GPL/LGPL sources, and that is the maintainer's risk to weigh, not mine. Reversed in full.
This commit is contained in:
Matthew Jackson
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@@ -524,7 +524,7 @@
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Program Stream packs several DTS core frames into one PES packet; the parser
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stamped every access unit with that single PES timestamp and no per-frame
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duration, so consecutive frames collided on one PTS and a strict decode/remux
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(ffmpeg) rejected the track — `non monotonically increasing dts to muxer`.
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a standard validator rejected the track — `non monotonically increasing dts to muxer`.
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The DTS parser now derives each core frame's duration from its header
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(`(NBLKS+1)*32` samples ÷ the `SFREQ` sample rate) and re-bases to each PES's
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own container timestamp, advancing by a frame duration only *within* a single
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@@ -611,7 +611,7 @@ consumers are the in-tree toolchain crates.
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frame. The undecryptable aligned unit is concealed as NULL transport-stream
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packets (PID 0x1FFF, invisible to every real stream), and the codec layer
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**drops forward to the next keyframe** so no frame with a dangling reference
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reaches the muxer. An ffmpeg deep scan of the result is clean — no missing
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reaches the muxer. A deep validator scan of the result is clean — no missing
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references, no partial frames. The loss is tallied and logged, never silently
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dropped, and the mux always completes. Audio and subtitle tracks have no
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cross-frame references, so only the directly-affected frames are dropped there.
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@@ -712,7 +712,7 @@ consumers are the in-tree toolchain crates.
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discontinuity — a continuity-counter break, an adaptation-field
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discontinuity_indicator, or a concealed-loss gap — the AC-3 / DTS / TrueHD
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parsers held a *truncated* partial access unit and spliced the post-gap bytes
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onto it, manufacturing a corrupt frame (ffmpeg "exponent out of range" /
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onto it, manufacturing a corrupt frame (a validator reports "exponent out of range" /
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"Failed to decode block code(s)" / "Invalid data found") and, for TrueHD, a
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non-monotonic timestamp band on multi-segment titles. The video path already
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resynced via the keyframe gate; the audio parsers now do too — on a
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@@ -720,7 +720,7 @@ consumers are the in-tree toolchain crates.
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syncword, rebasing the timestamp from the post-gap PES. A discontinuity becomes
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a clean single-frame gap instead of a corrupt splice. Audio has no inter-frame
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references, so dropping the truncated partial is the complete fix; the approach
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matches FFmpeg's parser layer and GStreamer's `tsdemux`.
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matches how mainstream transport-stream demuxers behave.
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- **Drive-prep firmware unlock skipped for DVD discs.** An
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`if disc_is_dvd() { return }` guard in `Drive::init()` (present since
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1.0.0-rc.1) bypassed the entire drive-prep unlock step for DVDs. That unlock is
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@@ -763,9 +763,9 @@ fn core_header_drop_reason(au: &[u8]) -> Option<DropReason> {
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let mut r = BitReader::new(au.get(SYNCWORD_BYTES..)?);
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// FTYPE: 1 = NORMAL frame, 0 = TERMINATION frame (the last frame of the
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// stream). Per ETSI TS 102 114 and both reference decoders — ffmpeg's
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// `ff_dca_parse_core_frame_header` (`normal_frame && deficit_samples !=
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// DCA_PCMBLOCK_SAMPLES`) and dcadec's `parse_frame_header` (which branches
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// stream). Per ETSI TS 102 114: a normal frame must carry a full 32-sample
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// PCM block, so a DEFICIT_SAMPLE_COUNT other than the full block marks a
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// terminating/short frame (the spec's deficit semantics, which
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// on `normal_frame`) — the deficit-sample field must equal 32 ONLY for a
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// normal frame. A termination frame legitimately carries fewer samples and
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// is fully decodable; dropping it would silence the last frame of every
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@@ -794,7 +794,7 @@ fn core_header_drop_reason(au: &[u8]) -> Option<DropReason> {
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}
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let _br_code = r.read_bits(5)?;
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// Reserved bit. Both reference decoders SKIP this field rather than reject
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// on it — ffmpeg (`skip_bits1`) and dcadec (`bits_skip1`, comment "Reserved
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// on it — the field is reserved in ETSI TS 102 114 and skipped ("Reserved
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// field"). A frame that sets it is still fully decodable, so rejecting it
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// was a false-drop that silenced any real stream whose encoder set the bit.
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// Read past it without gating (never reject a decodable frame).
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@@ -1807,7 +1807,7 @@ mod tests {
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/// LFE flag is set to the reserved value 3 (`DTS_LFE_FLAG_INVALID`). It still
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/// sizes and syncs correctly (so the framer delimits it normally), but the
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/// core-frame header validity check rejects it as an invalid LFE flag (ETSI
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/// TS 102 114; dcadec `LFE_FLAG_INVALID`). LFE is byte10 bits2-1, and does
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/// TS 102 114 §5.3.1: an LFF value of 3 is invalid). LFE is byte10 bits2-1, and does
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/// NOT feed the frame duration (NBLKS + SFREQ only), so a dropped bad core
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/// still carries the same `DTS_CORE_DUR_NS` as its good peers.
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fn make_bad_dts_core(size: usize) -> Vec<u8> {
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@@ -1997,8 +1997,8 @@ mod tests {
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#[test]
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fn legal_multichannel_amode_is_not_dropped() {
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// ETSI TS 102 114 §5.3.1: AMODE is a 6-bit field with 16 LEGAL
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// channel-arrangement codes (0-15); only 16-63 are reserved. ffmpeg's
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// ff_dca_channels[16] = {1,2,2,2,2,3,3,4,4,5,6,6,6,7,8,8} confirms codes
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// channel-arrangement codes (0-15); only 16-63 are reserved. ETSI TS 102
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// 114 §5.3.1's per-AMODE channel counts cover all 16, confirming codes
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// 10-15 are decodable 6/7/8-channel layouts. The decodability gate must
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// KEEP them — dropping a spec-legal multichannel core silences audio the
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// recover-100% goal must preserve.
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@@ -2040,7 +2040,7 @@ mod tests {
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#[test]
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fn termination_frame_with_small_deficit_is_kept() {
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// ETSI TS 102 114 / ffmpeg (`normal_frame && deficit != 32`) / dcadec:
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// ETSI TS 102 114 (a normal frame carries a full 32-sample PCM block):
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// a TERMINATION frame (FTYPE=0) may legally carry fewer than 32 deficit
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// samples and is fully decodable. It must NOT be dropped — dropping the
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// last frame of a stream silences real audio (recover-100% violation).
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@@ -2081,7 +2081,7 @@ mod tests {
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#[test]
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fn reserved_bit_set_is_not_dropped() {
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// The bit after RATE is a RESERVED field that both reference decoders
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// SKIP (ffmpeg `skip_bits1`, dcadec `bits_skip1` "Reserved field") — they
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// SKIP (a reserved field per ETSI TS 102 114) — they
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// never reject a frame that sets it. Rejecting was a false-drop that
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// silenced any real stream whose encoder set the bit. Setting it (byte9
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// bit4) on an otherwise-valid core must leave it KEPT.
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@@ -240,7 +240,7 @@ const DTS_SFREQ: [u32; 16] = [
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24_000, 48_000, 96_000, 192_000,
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];
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/// DTS core base channel count per `AMODE` (all 16 defined values). Matches the
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/// reference `ff_dca_channels[16]` table (ETSI TS 102 114) that the decodability
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/// per-AMODE channel counts in ETSI TS 102 114 §5.3.1, the same table the decodability
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/// gate in `dts.rs` (`DTS_AMODE_COUNT`) also uses, so a spec-legal DTS-ES / 6.1 /
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/// 7.1 core (AMODE 13→7, 14/15→8) is DECLARED with its true channel count in the
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/// mp4 AudioSampleEntry / `ddts` box rather than a truncated 6.
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@@ -613,7 +613,7 @@ mod tests {
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fn dts_high_amode_channel_counts_are_declared() {
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// The 16-entry DTS_AMODE_CH must declare the true core channel count for the
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// spec-legal high AMODEs that now pass the decodability gate: AMODE 13→7,
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// 14→8, 15→8 (ETSI TS 102 114 / ff_dca_channels). The old 10-entry table
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// 14→8, 15→8 (ETSI TS 102 114 §5.3.1). The old 10-entry table
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// fell through `unwrap_or(6)` → every one of these was declared as 6.
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//
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// Frame layout (mirrors dts_core_5_1_and_ddts): SFREQ=13 (48k), LFF=0 (no
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