feat(mp4): decode QuickTime audio sample entries .mp3, lpcm, twos, and sowt - #554
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August 18, 2026 16:48
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@nchitkara-xai Thanks for the PR. Looks good. |
…d sowt These QuickTime sample description names use the standard sound sample description layout, but fell through to UnknownBox, so their channel count, sample size, and sample rate were unreachable without hand parsing. Register them with the audio sample entry decoder and expose them as StsdBox.Mp3 and StsdBox.QtPcm. Since these names decoded as UnknownBox before, a body that does not parse as a sound sample description falls back to UnknownBox instead of failing the file, and the StsdBox.AddChild type assertions for the new names tolerate that fallback instead of panicking on it.
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Problem
The QuickTime audio sample entries
.mp3,lpcm,twos, andsowtfallthrough to
UnknownBox, so their sound description fields (channel count,sample size, sample rate, and the version 1/2 extensions — lpcm entries carry
a version 2 description in practice) are unreachable without hand-parsing.
Fix
Register the four names in both dispatch tables so they decode as
AudioSampleEntryBox, reachable asStsdBox.Mp3andStsdBox.QtPcm(oneshared pointer for the three PCM names, like
AvcX/HvcX— checkType()).Two safeguards keep hostile or odd files decodable:
UnknownBoxwith its bytes verbatim, so nothing that decoded before stopsdecoding;
StsdBox.AddChildcases for these names use comma-ok assertions totolerate that fallback, so an stsd containing e.g. a truncated
.mp3entry decodes cleanly instead of panicking.
Note that a
.mp3entry carries no esds; its codec facts live in the sounddescription fields themselves.
Tests
All four names decode with correct fixed fields and round-trip; an lpcm
version 2 description populates
QuickTimeV2; a truncated body falls back toUnknownBoxbyte-verbatim; and an stsd containing that truncated entrydecodes cleanly on both decode paths.
go test ./...,go vet,gofmt,golangci-lintpass.