可以在AVPlayer中添加一个KVO观察者，监听AVPlayerItem的status属性和loadedTimeRanges属性。当status变为AVPlayerStatusReadyToPlay时，开始播放。当loadedTimeRanges的duration大于视频总时长的某个百分比（例如0.7），说明已经缓存了足够的数据，可以继续播放。如果缓存的时间小于0.7倍的视频总时长，则暂停播放，等待缓存完成。在等待时，通常会显示一个加载指示器，以告知用户视频正在加载中。

示例代码如下：

let player = AVPlayer(url: videoURL)

player.addObserver(self, forKeyPath: #keyPath(AVPlayerItem.status), options: [.old, .new], context: nil)
player.addObserver(self, forKeyPath: #keyPath(AVPlayerItem.loadedTimeRanges), options: [.old, .new], context: nil)

// 播放视频
player.play()

// KVO通知回调
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    
    if keyPath == #keyPath(AVPlayerItem.status) {
        if let status = change?[.newKey] as? Int, let player = object as? AVPlayer {
            if status == AVPlayer.Status.readyToPlay.rawValue {
                player.play()
            }
        }
    }
    
    if keyPath == #keyPath(AVPlayerItem.loadedTimeRanges) {
        if let timeRange = (object as? AVPlayerItem)?.loadedTimeRanges.first?.timeRangeValue {
            let loadedDuration = CMTimeGetSeconds(CMTimeAdd(timeRange.start, timeRange.duration))
            let totalDuration = CMTimeGetSeconds(player.currentItem?.duration ?? .zero)
            if loadedDuration / totalDuration > 0.7 {
                player.play()
            }
        }
    }
}