Описание тега avplayerlayer
AVPlayerLayer is a subclass of CALayer to which an AVPlayer object can direct its visual output.
During playback, AVPlayer may compensate for temporal drift between its visual output and its audible output to one or more independently-clocked audio output devices by adjusting the timing of its associated player layers. The effects of these adjustments are usually very small; however, clients that wish to remain entirely unaffected by such adjustments may wish to place other layers for which timing is important into independently timed subtrees of their layer trees.
You can create arbitrary numbers of player layers with the same AVPlayer object. Only the most-recently-created player layer will actually display the video content on-screen.
Click Here for Apple documentation of AVPlayerLayer.