从 tvOS swift 上的 m3u8 播放列表中选择 AVPlayer 中的频道和字幕

Question

遵循 Apple 的官方文档：[https://developer.apple.com/documentation/avfoundation/media_playback_and_selection/selecting_subtitles_and_alternative_audio_tracks]

self.playerStatusObserver = player.observe(\.currentItem?.status, options: [.new,.old]{ (player, change) in
switch (player.status) {
   case .readyToPlay:
     player.appliesMediaSelectionCriteriaAutomatically = false
     for characteristic in player.currentItem!.asset.availableMediaCharacteristicsWithMediaSelectionOptions {
         print("\(characteristic)")

           // Retrieve the AVMediaSelectionGroup for the specified characteristic.
           if let group = player.currentItem!.asset.mediaSelectionGroup(forMediaCharacteristic: characteristic) {
               // Print its options.
               for option in group.options {
                   print("  Option: \(option.displayName)")
               }
           }
       }

player.currentItem!.asset.availableMediaCharacteristicsWithMediaSelectionOptions没有项目。

尝试了很多情况，但是player.currentItem?.tracks只有两个轨道（视频和音频），即使流有更多的音频轨道。

如何使用标准的 AVPlayer 和 AVFoundation 框架从 m3u8 流中选择音轨和字幕？

Answer 1

您的代码依赖于准备播放的当前项目来访问availableMediaCharacteristics 。 它可能发生availableMediaCharacteristics实际上还没有上市的那一刻，除非你创建与物业玩家项目automaticallyLoadedAssetKeys参数：

AVPlayerItem(asset: asset, automaticallyLoadedAssetKeys: ["availableMediaCharacteristicsWithMediaSelectionOptions"])

您可以在以下页面上找到有关此的更多信息： https : //developer.apple.com/documentation/avfoundation/avplayeritem/1388633-automaticallyloadedassetkeys

根据您的用例，您也可能更喜欢异步加载媒体特征，您可以使用以下代码执行此操作：

 func preloadAssetKeys() {
    let key = "availableMediaCharacteristicsWithMediaSelectionOptions"
    
    asset.loadValuesAsynchronously(forKeys: [key]) {
        [weak self] in
        guard let self = self else { return }

        var error: NSError? = nil
        switch self.asset.statusOfValue(forKey: key, error: &error) {
        case .loaded:
            // ℹ️ At this point is when availableMediaCharacteristics are actually available
            ()
        default:
            ()
        }
    }
}