Fix mdhd/mvhd version 1 (64-bit) atom parsing — half duration bug#2626
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tjiddy wants to merge 1 commit intoBorewit:masterfrom
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Fix mdhd/mvhd version 1 (64-bit) atom parsing — half duration bug#2626tjiddy wants to merge 1 commit intoBorewit:masterfrom
tjiddy wants to merge 1 commit intoBorewit:masterfrom
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Version 1 mdhd and mvhd atoms use 64-bit fields for creation time, modification time, and duration, shifting all subsequent field offsets by 12 bytes compared to version 0. The parser was hardcoded for version 0 offsets only, causing it to read the wrong bytes for timeScale and duration on version 1 atoms. This resulted in exactly half the correct duration being reported for M4B audiobook files that use version 1 mdhd atoms (typically files produced by Audible/Libation with 22050 Hz sample rate). The fix checks the version field and uses the correct offsets for each version. Adds a 64-bit SecondsSinceMacEpoch token for the larger timestamp fields in version 1 atoms.
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Summary
Fixes incorrect duration parsing for MP4/M4B files that use version 1 (64-bit)
mdhdandmvhdatoms. These atoms report exactly half the correct duration because the parser was hardcoded for version 0 field offsets only.Root Cause
The ISO 14496-12 spec defines two versions of
mdhd/mvhd:Version 1 shifts the
timeScalefield from offset 12 to offset 20, anddurationfrom offset 16 (4 bytes) to offset 24 (8 bytes). The parser read all fields at version 0 offsets regardless of version, causing it to read incorrect values from the middle of 64-bit fields.Evidence
Tested with 6 M4B audiobook files. All version 1 files reported exactly half duration; all version 0 files were correct:
Changes
MdhdAtom.get(): Check version field; use 64-bit offsets andUINT64_BEfor version 1MvhdAtom.get(): Same version-aware parsing (same bug, same fix)SecondsSinceMacEpoch64token for 64-bit timestamp fields in version 1 atomsTests
All 568 existing tests pass. No regressions.