Multi Selection
This can be used if tracks from multiple streams should be forwarded to ExoPlayer, so ExoPlayer can mux them together. This StreamSelection will be made into a MergingMediaSource. This stream selection will not depict which of the tracks contained in the StreamSelection should be muxed together by ExoPlayer. This MultiSelection only depicts that at least all the tracks that should be played are contained.
The information to pick the actual tracks out of the available tracks within this selection bust be given to ExoPlayer through another mechanism. (You see this is still TODO).