There are two main changes that need to be made:
1. Whenever we determine the next ad to play, we need to select a
server-side inserted ad even if it has been played already (because
it's part of the stream).
2. When the Timeline is updated in the player, we need to avoid changes
that would unnecessarily reset the renderers. Whenever a Timeline
change replaces content with a server-side inserted ad at the same
position we can just keep the existing MediaPeriod and also if the
duration of the current MediaPeriod is reduced but it is followed by
a MediaPeriod in the same SSAI stream, we can don't need to reset
the renderers as we keep playing the same stream.
PiperOrigin-RevId: 373745031
795210d7bc