QuickTime chapter samples run back to back from media time 0, so when the
first chapter starts after 0, QtChapterList::write() prepends an untitled
placeholder sample to keep the absolute start times. TagLib's own reader
strips it again, but the chapter track's edit list played the whole media
from time 0, so AVFoundation and ffmpeg listed the placeholder as an
untitled first chapter.
The edit list now begins with an empty edit spanning the placeholder,
followed by the media from the first written chapter. The placeholder
sample is kept, so readers which ignore edit lists see the same chapters
as before. A list starting at 0 still gets a single edit.
testQTChapterListNonZeroFirstChapterEditList writes chapters at 1 s and
2 s and checks the chapter track's elst: an empty edit (media time -1) of
one second in the mvhd timescale, then the remaining duration from media
time one second. It also checks that a list starting at 0 gets a single
edit from media time 0, and that qtChapters() reads back exactly the
written chapters in both cases.
Ryan FrancesconiandGitHub
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