When creating a faststart file, qtmux has to take into account that
any 32 bit stco atom may need to be converted into its 64 bit version
due to the offset that is added before the mdat data by the moov atom,
the extra atoms and the mdat header. If a stco atom is converted into
co64, the chunk offset of all stco and co64 atoms has to be increased,
which in turn may also cause that other stco atoms need to be converted
into co64, modifying the chunk offsets again.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/9102>
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