ios - AVPlayer 和 AVPlayerItem 状态什么时候改变？

Question

我正在使用 AVFoundation 在 flutter 中开发一个音乐播放器插件，我想在 iOS 和 Android 上创建一个统一的界面。

我想捕获 AVPlayer 可能抛出的错误，例如，给定的 AVPlayerItem 无效(包含 URL不受支持的文件，例如 png 文件)。

我希望 AVPlayer.replace() 抛出异常或改变 AVPlayerItem 或 AVPlayer 的状态或至少一些相关通知在 NSNotificationCeter 上。我试着听/观察所有这些，但没有一个报告任何类型的错误。事实上，AVPlayer 报告了“准备播放”状态。

    mediaPlayer = AVPlayer();
    playerItem = AVPlayerItem(url: URL(fileURLWithPath: Bundle.main.path(forResource: "image", ofType: "png")!))

    playerItem?.addObserver(self, forKeyPath: #keyPath(AVPlayerItem.status), options: [.old, .new], context: &playerItemContext)
    mediaPlayer?.addObserver(self, forKeyPath: #keyPath(AVPlayer.status), options: [.old, .new], context: &mediaPlayerContext)

    mediaPlayer?.replaceCurrentItem(with: playerItem); // this changes player status to - "ready-to-play"
    mediaPlayer?.play() // this does not report anything

我是一名 android 开发人员，无法理解 AVPlayer 的工作原理。我怎样才能做到这一点？

注意:我不能使用 AVAudioPlayer，因为文档说在从网络或可能有延迟的源播放音乐时不应使用它。

self.mediaPlayer?.replaceCurrentItem(with: nil)
self.mediaPlayer?.play()

即使这段代码也不会产生错误

Answer 1

private func addObserverPlayerItem()
    {
        if let playerItem = self.player?.currentItem{
            playerItem.addObserver(self, forKeyPath: "playbackBufferEmpty", options: .new, context: nil)
            playerItem.addObserver(self, forKeyPath: "playbackLikelyToKeepUp", options: .new, context: nil)
            playerItem.addObserver(self, forKeyPath: "playbackBufferFull", options: .new, context: nil)
            playerItem.addObserver(self, forKeyPath: "loadedTimeRanges", options: [.new], context: nil)
            self.player?.addObserver(self, forKeyPath: #keyPath(AVPlayer.currentItem.status), options: [.new, .initial], context: nil)
            self.player?.addObserver(self, forKeyPath: #keyPath(AVPlayer.status), options: [.new, .initial], context: nil)
        }
    }

override public func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if object is AVPlayerItem {
            switch keyPath {

            case "loadedTimeRanges":

                let duration = self.currentItem?.totalBuffer() ?? 0
                let totalduration = currentItem?.asset.duration
                self.videoControll?.slider.bufferEndValue = totalduration?.seconds ?? 0
                self.videoControll?.slider.bufferStartValue = (duration) / (totalduration?.seconds ?? 1)
                print((duration) / (totalduration?.seconds ?? 1))

            case "playbackBufferEmpty":
                // Show loader
                self.activityIndicator?.startAnimating()

            case "playbackLikelyToKeepUp":
                // Hide loader
                self.activityIndicator?.stopAnimating()

            case "playbackBufferFull":
                // Hide loader
                self.activityIndicator?.stopAnimating()
            case #keyPath(AVPlayer.currentItem.status):

                let newStatus: AVPlayerItem.Status
                if let newStatusAsNumber = change?[NSKeyValueChangeKey.newKey] as? NSNumber {
                    newStatus = AVPlayerItem.Status(rawValue: newStatusAsNumber.intValue)!
                } else {
                    newStatus = .unknown
                }
                if newStatus == .failed {
                    NSLog("SA Detected Error: \(String(describing: self.player?.currentItem?.error?.localizedDescription)), error: \(String(describing: self.player?.currentItem?.error))")
                }
            case #keyPath(AVPlayer.status):
                print()
            case .none:
                self.activityIndicator?.stopAnimating()
            case .some(_):
                self.activityIndicator?.stopAnimating()
            }
        }
    }