Support pausing at a frame-accurate position

Hello, I have a question to consult
My English is not very good, please forgive me

I will be more MediaSource add ConcatenatingMediaSource ,
I want to listen CurrentWindowIndex to finish playing

```
@Override
public void onLoadingChanged(boolean isLoading) {
int curTime = (int) (player.getCurrentPosition() );
int time = (int) (player.getBufferedPosition() );
System.out.println("播放: onLoadingChanged " + curTime + "--->" + time);
if (time != 0 && curTime == time) {
player.setPlayWhenReady(false)；
}
}
}
```
I can't do it that way