Since the sample map/track buffer now iterates samples in batches corresponding
to each coded frame group, the logic to feed the tracks is simpler. For media
without delta frames, it's a special case where the coded frame groups are all
size 1.
Now, all it does is skip data until the keyframe group containing the seek point
is found, then feed the track queue with the current sample and all future
samples until EOS or cancellation.
Resync of the iterator when the underlying track is modified is not necessary
because the outer loop attempts to resume feeding track data from where it was
interrupted in case of modification.
Also, the track feed task struct now holds a weak ref to its parent source
buffer to allow the task to cancel itself in any situation where the source
buffer is destroyed before the task is shut down.
Media parsing activity in the append pipeline no longer triggers ready state
recalculation on the msesrc since the msesrc now has a background task that
updates the ready state periodically when it's active which is more efficient in
cases where there is a high volume of samples being processed by the media
parser.
Finally, updated to adapt to track buffer API changes. Some functions previously
passed in a lower bound for sample timestamps. Now the source buffer is
responsible for clipping samples within a desired range of time.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8512>
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