Before this CL, the buffer adjustment (which allows to convert from
ExoPlayer time to VideoGraph time) was added to the frame timestamps
before feeding them to the VideoGraph, and then subtracted at the
VideoGraph output. The playback position and stream start position used
for rendering were in ExoPlayer time.
This doesn't work for multi-sequence though because the adjustment might
be different depending on the player (after a seek for example).
To solve this problem, this CL handles rendering in VideoGraph time
instead of ExoPlayer time. More concretely, the VideoGraph output
timestamps are unchanged, and the playback position and stream start
position are converted to VideoGraph time.
PiperOrigin-RevId: 752260744
0f08c97221