Two fixes for video freeze during recording:
1. Video capture loop (30fps) moved from main-thread Timer to a
dedicated DispatchSourceTimer on 'miniplayer.videoCapture' queue.
copyPixelBuffer() on the main thread was competing with AVPlayer's
rendering pipeline for CPU time, causing frame stalls.
2. AVPlayerItemDidPlayToEndTime observer now checks notification.object
against player.currentItem. Previously object:nil caught stale
notifications from replaced items, causing spurious playNext() calls
that interrupted playback (visible as duplicate playIndex in logs).
yumoqing
f68476d57f