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…). An MP4 whose audio sample entry type is lpcm with version 0 or 1 aborted the process while parsing the stsd atom. is_pcm_codec() returns true for the lpcm atom type at every version, but pcm_codec_id() only maps fixed PCM atom types and returns CODEC_ID_NULL_AUDIO for lpcm. The version 0 and 1 paths then called bytes_per_pcm_sample() with the null codec id, which fell through to unreachable!(). The PCM format of an lpcm entry is only described by the version 2 extension fields, so an lpcm entry at version 0 or 1 is invalid. The version 0 and 1 arms now reject a null codec id with a decode error, matching the version 2 arm that already guards on it. Fixes pdeljanov#560.
baylesj
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Oct 5, 2026
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| if entry.codec_id == CODEC_ID_NULL_AUDIO { | ||
| return decode_error("isomp4: lpcm audio sample entry must be version 2"); | ||
| } |
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Clean guard matching the v2 CODEC_ID_NULL_AUDIO check below.
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Issue
Fixes #560 — an MP4 whose audio sample entry type is
lpcmwith version 0 or 1 aborts the process while parsing thestsdatom.Root cause
is_pcm_codec()(symphonia-format-isomp4/src/atoms/stsd.rs) returnstrueforAtomType::AudioSampleEntryLpcmat every sample entry version, because in version 2 the atom type for PCM data is always LPCM. However,pcm_codec_id()only maps the fixed PCM atom types and returnsCODEC_ID_NULL_AUDIOforlpcm. The version 0 (:216) and version 1 (:249) arms then callbytes_per_pcm_sample(CODEC_ID_NULL_AUDIO), which has no arm for the null codec and falls through tounreachable!()at:381:Reproduced end-to-end: a minimal MP4 (
ftyp+moov/trak/mdia/minf/stbl/stsdwith anlpcmsample entry at version 0) abortsIsoMp4Reader::try_newon current main.Fix
The PCM format of an
lpcmentry is only described by the version 2 extension fields, so anlpcmentry at version 0 or 1 is invalid. Both version arms now rejectCODEC_ID_NULL_AUDIOwith a decode error before reachingbytes_per_pcm_sample, matching the version 2 arm that already guards on the null codec id.Verification
lpcmv0 and v1 sample entries panic atstsd.rs:381(unreachable!()). Fixed: both returnDecodeError("isomp4: lpcm audio sample entry must be version 2").stsd.rs:lpcmv0/v1 rejected,lpcmv2 accepted,sowtv0 accepted (fixed-codec PCM atom types still parse).cargo test -p symphonia-format-isomp4: 4 passed, 0 failed.cargo clippy -p symphonia-format-isomp4 --all-targets: clean;cargo check --all-targets: clean.Disclosure: this PR was prepared with AI assistance (Devin) and verified locally before submission.