Allow setting playback parameters for a future position (including media item transitions)

Hi,

I'm using ConcatenatingMediaSource to play a sequence of videos, some of which need to be played at a different speed / pitch, while keeping a smooth playback.

The doc for Player#setPlaybackParams() states that "Playback parameters changes may cause the player to buffer.", so an approach that "monitors playback progress" and applies any updated params when necessary would not work well here.

I also noticed digging through setPlaybackParams() that any pending samples are *not* flushed out of the AudioTrack, so when calling this method during playback, you can still hear samples transformed with previous settings for a few milliseconds.

Is there any mechanism that I could use to let the player know up front that when buffering from timestamp t1, it should start doing so using a different set of playback params?

I'm currently on ExoPlayer 2.8.

Would appreciate any tips on this. Thanks!