Eyevinn / mp4ff / 33440988488

82%

master: 83%

Pull #556

github

feat(mp4): add QuickTime-to-ISO audio sample entry normalization

A QuickTime-shaped audio sample entry (sound sample description version
1 or 2, or an esds wrapped in a wave box) is not the plain version 0
form that isom-branded files expect, so remuxing QuickTime audio needs
the sample entry rewritten.

Add AudioSampleEntryBox.NormalizeQuickTime, which rewrites such an
entry in place, like RemoveEncryption does for encrypted entries: the
esds becomes a direct child (a direct esds wins over a wave-wrapped
one), the wave box and the QuickTime version, revision level, and
vendor are dropped, and a version 2 entry gets its channel count,
sample size, and sample rate (rounded to the nearest integer) restored
from the version 2 fields. QuickTime residue in the reserved fields of
a version 0 entry is cleared the same way. A rate above 65535 Hz does
not fit the 16.16 sample rate field and leaves 0, as ffmpeg writes; the
authoritative rate is in the esds AudioSpecificConfig.

The rewrite fails closed: entries without a reachable esds, whose
decode parameters live elsewhere, keep their QuickTime shape, and so
does an entry whose wave box holds anything besides its recognized
decoder-init atoms (frma, esds, the terminator, and the stub named
after the entry), since dropping such a wave box would silently lose
content.

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