When a renderer is pre-enabled (while another playback is still
ongoing), we pass mayRenderStartOfStream=false to Renderer.enable.
This ensures we don't show any first frames while the previous media
is still playing.
Currently, we never tell the renderer when we actually stop playing
the previous media so that it could render the start of the stream,
because we allow this as soon as the renderer is in STATE_STARTED and
we assume that we have to be in STATE_STARTED to make this stream
transition.
While this assumption is true, there are also cases where we can't
start the renderers because they are not ready yet and the video
renderer can't become ready because it didn't render its first frame.
This effectively blocks playback forever.
The most direct way of solving this, is to tell the renderer that
playback has transitioned and that it is now allowed to render the
start of the stream. This means it can never get blocked as described
above.
PiperOrigin-RevId: 547727347
d8498f3ecb