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?

[macneko-ayu]

AVPlayerのストリーミング再生時のバッファ切れの確認方法

[iRSS]

AVPlayerに追加したAVPLayerItemのストリーミング切れを確認する方法と、復帰方法。