使用 AVPlayerLooper 循环播放多个视频

Question

我一直试图弄清楚如何使用AVPlayerLooper 循环播放多个视频，但他们的templateItem 采用AVPlayerItem 类型的参数而不是[AVPlayerItem]。我目前正在使用AVQueuePlayer 来显示视频，但我需要循环播放它。

到目前为止，这是我的代码：

class MyVC: UIViewController {

     @IBOutlet weak var playerView: UIView!

     lazy var backgroundVideoPlayer = AVQueuePlayer()

     // View Controller related code (viewDidLoad, etc.) is taken out for brevity.

     private func loadBackgroundVideosRandomly() -> [AVPlayerItem] {
         let mainBundle = Bundle.main
         let movieURLs = [mainBundle.url(forResource: "Boop Burj Al Arab", withExtension: "mov"),
                          mainBundle.url(forResource: "Boop Dubai", withExtension: "mov"),
                          mainBundle.url(forResource: "Boop Dubai Clock", withExtension: "mov"),
                          mainBundle.url(forResource: "Boop Dubai Lake", withExtension: "mov")].shuffled()

         let items = movieURLs.map { AVPlayerItem(url: $0!) }
         return items
    }

    private func playBackgroundVideos() {
         let playerLayer = AVPlayerLayer(player: backgroundVideoPlayer)
         playerLayer.videoGravity = .resizeAspectFill
         playerLayer.frame = playerView.bounds
         playerView.layer.addSublayer(playerLayer)

         // Configure the player.
         backgroundVideoPlayer.seek(to: kCMTimeZero)
         backgroundVideoPlayer.actionAtItemEnd = .advance
   }
}

Answer 1

所以我通过观看 WWDC 2016 的一些演讲找到了解决方案，他们描述了跑步机模式并查看了示例代码。

本质上，您加载要播放的视频，然后使用 Key Value Observing 在播放视频时做出响应，然后将该播放的视频添加回堆栈的末尾。

首先创建一个协议：

protocol BackgroundLooper {
     /// Loops the videos specified forever.
     ///
     /// - Parameter urls: The url where the video is located at.
     init (urls: [URL])

     /// Starts looping the videos in a specified layer.
     ///
     /// - Parameter layer: The layer where the video should be displayed.
     func start(in layer: CALayer)

     /// Stops the video playback.
     func stop()
}

然后创建一个符合协议的BackgroundQueuePlayerLooper。

import AVFoundation

/// Repeats a set of videos forever (ideally for use in a background view).
class BackgroundQueuePlayerLooper: NSObject, BackgroundLooper {

    // MARK: - Observer contexts

    /// The context required for observing.
    private struct ObserverContexts {
        static var playerStatus = 0
        static var playerStatusKey = "status"
        static var currentItem = 0
        static var currentItemKey = "currentItem"
        static var currentItemStatus = 0
        static var currentItemStatusKey = "currentItem.status"
        static var urlAssetDurationKey = "duration"
        static var urlAssetPlayableKey = "playable"
    }

    // MARK: - Properties

    private var player: AVQueuePlayer?
    private var playerLayer: AVPlayerLayer?
    private var isObserving = false
    private let videoURLs: [URL]

    // MARK: - Initialization

    required init(urls: [URL]) {
        self.videoURLs = urls
    }

    // MARK: - Looper

    func start(in layer: CALayer) {
        stop()

        player = AVQueuePlayer()
        player?.externalPlaybackVideoGravity = .resizeAspectFill

        playerLayer = AVPlayerLayer(player: player)
        playerLayer?.videoGravity = .resizeAspectFill

        guard let playerLayer = playerLayer else { fatalError("There was an error creating the player layer!") }
        playerLayer.frame = layer.bounds
        layer.addSublayer(playerLayer)

        let assets = videoURLs.map { AVURLAsset(url: $0) }
        assets.forEach { player?.insert(AVPlayerItem(asset: $0), after: nil) }

        startObserving()
        player?.play()
    }

    func stop() {
        player?.pause()
        stopObserving()

        player?.removeAllItems()
        player = nil

        playerLayer?.removeFromSuperlayer()
        playerLayer = nil
    }

    // MARK: - Key value observing

    /// Starts observing the player.
    private func startObserving() {
        guard let player = player else { return }
        guard !isObserving else { return }

        player.addObserver(self, forKeyPath: ObserverContexts.playerStatusKey, options: .new, context: &ObserverContexts.playerStatus)
        player.addObserver(self, forKeyPath: ObserverContexts.currentItemKey, options: .old, context: &ObserverContexts.currentItem)
        player.addObserver(self, forKeyPath: ObserverContexts.currentItemStatusKey, options: .new, context: &ObserverContexts.currentItemStatus)

        isObserving = true
    }

    /// Stops observing the player.
    private func stopObserving() {
        guard let player = player else { return }
        guard isObserving else { return }

        player.removeObserver(self, forKeyPath: ObserverContexts.playerStatusKey, context: &ObserverContexts.playerStatus)
        player.removeObserver(self, forKeyPath: ObserverContexts.currentItemKey, context: &ObserverContexts.currentItem)
        player.removeObserver(self, forKeyPath: ObserverContexts.currentItemStatusKey, context: &ObserverContexts.currentItemStatus)

        isObserving = false
    }

    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if context == &ObserverContexts.playerStatus {
            guard let newPlayerStatus = change?[.newKey] as? AVPlayerStatus else { return }
            guard newPlayerStatus == .failed else { return }
            // End looping since player has failed
            stop()
        } else if context == &ObserverContexts.currentItem {
            guard let player = player else { return }
            // Play queue emptied out due to bad player item. End looping.
            guard !player.items().isEmpty else { stop(); return }

            /*
             Append the previous current item to the player's queue. An initial
             change from a nil currentItem yields NSNull here. Check to make
             sure the class is AVPlayerItem before appending it to the end
             of the queue.
             */
            guard let itemRemoved = change?[.oldKey] as? AVPlayerItem else { return }
            itemRemoved.seek(to: kCMTimeZero, completionHandler: nil)
            stopObserving()
            player.insert(itemRemoved, after: nil)
            startObserving()
        } else if context == &ObserverContexts.currentItemStatus {
            guard let newPlayerItemStatus = change?[.newKey] as? AVPlayerItemStatus else { return }
            guard newPlayerItemStatus == .failed else { return }
            // End looping since player item has failed.
            stop()
        } else {
            super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
        }
    }
}

本质上，我们设置了AVPlayer 和AVPlayerLayer 对象。然后 KVO 会监听视频何时播放完毕并将其添加到要播放的视频的末尾。

Answer 2

AVPlayerLooper 将播放器作为第一个参数，所以你可以这样：

let myPlayer = AVQueuePlayer([AVPlayerItem])

AVPlayerLooper(player: myPlayer, templateItem: oneoftheitems)

Answer 3

对于仍在寻找答案的任何人，Ray Wenderlich 来救援：

https://www.raywenderlich.com/5191-video-streaming-tutorial-for-ios-getting-started#toc-anchor-009

基本上，观察队列中何时还有一个 playerItem，然后重新插入所有 playerItem。