Check whether there is frames dropping in the stream and skip it
Created by: WeiRen1991
It is very common case that there is frames dropping in a video stream. And a robust player should tolerate this case.
I have added some logic that if the player stalls for a while, the player will check whether there is small discontinuity in the buffer. And if there is, it will skip the gap.
And the code often consider some corner cases. If the loss is at the end of the stream, switch the stream. And considered if the loss concurrently happens in video, audio and subtitles.