使用KVO观察AVPlayer的timeControlStatus属性，以便检测播放状态的更改。

代码示例：

// 初始化AVPlayer
let player = AVPlayer(url: videoURL)

// 添加KVO观察者
player.addObserver(self, forKeyPath: "timeControlStatus", options: [.new, .old], context: nil)

// 实现KVO观察方法
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if keyPath == "timeControlStatus" {
        guard let newStatusAsNumber = change?[.newKey] as? NSNumber, let oldStatusAsNumber = change?[.oldKey] as? NSNumber else {
            return
        }
        
        let newStatus = AVPlayer.TimeControlStatus(rawValue: newStatusAsNumber.intValue)
        let oldStatus = AVPlayer.TimeControlStatus(rawValue: oldStatusAsNumber.intValue)
        
        if newStatus != oldStatus {
            if newStatus == .playing {
                // 当前正在播放
            } else if newStatus == .paused {
                // 当前已暂停
            } else if newStatus == .waitingToPlayAtSpecifiedRate {
                // 当前正在缓冲
            }
        }
    }
}