Mutation testing over src/mux/. No production change — 49 survivors
killed, all proven red before green.
The MP4 composition-time chain was entirely unconstrained: VideoTiming::ctts,
build_ctts and parse_ctts could each return a constant and the suite
stayed green. Confirmed on HEAD: build_ctts -> vec![] passes all 1,220
mux tests. A demuxed B-frame title presenting in decode order would
have shipped.
The cause is a test whose name asserts coverage its body does not
deliver — stts_and_ctts_expand builds an stts box and never touches
ctts, and write_then_read_round_trip asserts sample sizes and keyframe
flags but not one PTS. Same shape as the set_speed forwarding finding,
different disguise.
mlp_num_substreams / mlp_substr_header_size: every TrueHD fixture in
the crate uses one substream and no extraword, so both could return a
constant and agree with all of them. These position mlp_parity_ok's
window over the AU header, so a constant mis-windows the parity check
on exactly the multi-substream AUs that carry 7.1 and Atmos.
CodecPrivate absent vs empty: mkv.rs writes Some(bytes) verbatim and
omits the element on None (RFC 9559 5.1.4.1.24), so a zero-length Some
emits a track header asserting the config IS empty. Four parsers could
return Some(vec![]) before any frame.
Also: mandatory ISO/IEC 14496-12 boxes (tkhd, vmhd, smhd, dinf, mdhd)
could each build empty; HEVC num_extra_slice_header_bits (H.265 7.3.2.3)
was never non-zero in any fixture, so the slice-type offset skip was
unexercised; chapter names from the disc go straight into
<ChapterString> and the & escape must run first; a stray 0x47 in a
payload must not latch a TS resync.
Documented as equivalent rather than killed: CodecParser::flush and the
three parser flush bodies that differ from the mutant only by a tracing
call, and DropTally::log_summary.
Multi-round audit of the decrypt/AACS/mux-codec refactor. Fixes, in
descending severity:
- mux/mp4/read.rs: bound untrusted-input allocations. `sample_budget`
now also capped by file_len (a fixed-size stsz claiming count=u32::MAX
can't inflate the Vec<SampleRef> past the file's own size); trak scan
capped at MAX_TRACKS matches; find_box() takes only the first match
(cap=1) instead of materializing every match. Removes dead find_boxes
wrapper.
- disc/mod.rs: merge_content_key_ranges now UNIONS same-key overlapping
ranges (coverage-preserving) instead of dropping the non-overlapping
tail, which silently left encrypted LBAs uncovered -> ciphertext
passthrough in the whole-disc sweep/patch map. Different-key overlap
(malformed) still dropped to keep the set disjoint.
- sector/decrypting.rs: remove dead unit_key_idx field + with_unit_key_idx
setter (vestigial from the pre-keymap trial-decrypt design; AACS is
map-only now). Fix stale docs.
- decrypt.rs / resolve.rs / error.rs / extract.rs: doc/comment drift from
the refactor (AacsKeyMap positive-map semantics, resolve_mux_key_map doc
reattachment, decrypt_sectors_in_content legacy-alias, E_MP4_INVALID
meaning, multi-CPS orphan by-design note).
Test coverage (all mutation-verified real):
- DTS NeedMore force-flush buffer bound; FLAC/MPEG-audio PTS carry-forward;
mp4 mdhd timescale=0 divide-by-zero guard, MAX_TRACKS cap, sample-count
file_len bound, MAX_ALLOC_BYTES cap under inflated file_len.
- resolve_fmts_key_map: extracted filter_addressable_segments,
resolve_tie_phase, fill_base_key_gaps as pure behavior-preserving
helpers, each unit-tested (segment filter, phase-tie arms, gap-fill
gaplessness over every extent).
mp4 demuxer (untrusted input): bound every allocation sized from a box
field (stsz/stco/stsc counts, stts/ctts run-lengths, per-sample and moov
sizes, plus an absolute cap so a sparse file can't inflate file_len);
guard the parse_stsd slice and a zero mdhd timescale; cap track count so
the per-track PID can't overflow; rewrite read_moov to handle size==0 /
size<8 / 64-bit largesize; parse esds/AudioSpecificConfig for AAC; write
tkhd duration in the movie timescale.
decrypt: resolve_mux_key_map now fails loud on an extent no key can
classify instead of inheriting the previous extent's key, so a keymap
never silently carries a wrong key; the sweep/patch key-fetch recovery
fails loud when a unit is still unresolved after the retry.
AACS: reject inverted forensic segments in both range builders; compare
the forensic index in u16 space so an out-of-range value can't truncate
onto a valid u8 index. RECOVERED_ERROR no longer latches the damage zone,
preserving the 30s wedge cooldown for a following hard error.
audio: AAC/MP2/MP3/FLAC carry the last PTS across a PES with no timestamp;
the DTS-HD extension-sync search is bounded to after the core; the MP4
16.16 sample-rate field saturates. demux_sink records the video reference
before the kind filter so audio:// / sub:// keep multi-clip PTS continuity
and the DELAY tag.
Remove a dead error variant and the AACS-unsupported-video code; codec
comments cite the primary format specs; assorted doc/naming fixes and
regression tests throughout.
Free-format MPEG-audio (bitrate_index 0) is a legal, decodable mode — the
decoder derives the frame size from the sync spacing. Dropping it was a
false positive on a clean stream, so it now passes the gate.
A damaged audio access unit is now dropped rather than muxed as a
decoder-choking glitch. Sync is preserved — a drop becomes a silence
gap, never a shift — and every drop is logged. Detection is per-codec,
each mirroring the format's authoritative integrity check:
DTS core-header validity gates
AC-3/E-AC-3 native frame CRC-16 + bitstream-id range
FLAC whole-frame CRC-16 residue
MP2/MP3 header sanity + free-format reject
AAC-ADTS header sanity (raw AAC passes through untouched)
TrueHD/MLP major-sync CRC-16 + AU parity; corrupt AUs drop forward
to the next major sync, since decode state carries
across access units
LPCM and video are excluded by design (no in-frame integrity data;
inter-frame prediction). A shared DropTally handles counting, logging,
and a whole-track fallback for a mostly-undecodable track.
Matthew Jackson