ios avplayer trigger streaming is out of buffer

I want to reconnect to the server when the streaming buffer is empty.

How can I trigger a method when the AVPlayer or AVPlayerItem buffer is empty?

I know there are playbackLikelyToKeepUp, playbackBufferEmpty and playbackBufferFull methods to check the buffer status, but those are not callbacks.

Are there any callback functions, or any observers I should add?