AVMutableComposition - 只播放第一首曲目 (Swift)

Question

我有一个 [AVAsset] 数组，我正在尝试将所有这些资产组合到一个资产中，以便我可以无缝播放视频（我尝试使用 AVQueuePlayer，但这不会播放资产无缝）。

以下是我到目前为止的内容，但是当我尝试播放最终作品时，它只播放第一首曲目，即使它显示它具有所有曲目并且总持续时间等于所有曲目的总和。

我是否遗漏了一个步骤，即使所有曲目似乎都在作曲中？如果 AVPlayerItem 有多个轨道，也许我需要以不同的方式处理 AVPlayer？

let playerLayer: AVPlayerLayer = AVPlayerLayer()
lazy var videoPlayer: AVPlayer = AVPlayer()

var videoClips = [AVAsset]()

let videoComposition = AVMutableComposition()
var playerItem: AVPlayerItem!
var lastTime: CMTime = kCMTimeZero

for clipIndex in videoClips {

    let videoCompositionTrack = videoComposition.addMutableTrackWithMediaType(AVMediaTypeVideo, preferredTrackID: Int32(kCMPersistentTrackID_Invalid))

    do {
        try videoCompositionTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, clipIndex.duration),
                                                  ofTrack: clipIndex.tracksWithMediaType(AVMediaTypeVideo)[0] ,
                                                  atTime: lastTime)
        lastTime = CMTimeAdd(lastTime, clipIndex.duration)
    } catch {
        print("Failed to insert track")
    }
}
print("VideoComposition Tracks: \(videoComposition.tracks.count)") // Shows multiple tracks

playerItem = AVPlayerItem(asset: videoComposition)
print("PlayerItem Duration: \(playerItem.duration.seconds)") // Shows the duration of all tracks together
print("PlayerItem Tracks: \(playerItem.tracks.count)") // Shows same number of tracks as the VideoComposition Track count

videoPlayer = AVPlayer(playerItem: playerItem)
playerLayer.player = videoPlayer
videoPlayer.volume = 0.0
videoPlayer.play()  // Only plays the first track

Answer 1

我能够找出最重要的问题的答案。为了一起播放所有剪辑，它们需要位于同一轨道中。为此，请将以下行移到 for 循环之外（之前）：

let videoCompositionTrack = videoComposition.addMutableTrackWithMediaType(AVMediaTypeVideo, preferredTrackID: Int32(kCMPersistentTrackID_Invalid))

这是完整的、更正后的代码：

let playerLayer: AVPlayerLayer = AVPlayerLayer()
lazy var videoPlayer: AVPlayer = AVPlayer()

var videoClips = [AVAsset]()

let videoComposition = AVMutableComposition()
var playerItem: AVPlayerItem!
var lastTime: CMTime = kCMTimeZero

let videoCompositionTrack = videoComposition.addMutableTrackWithMediaType(AVMediaTypeVideo, preferredTrackID: Int32(kCMPersistentTrackID_Invalid))

for clipIndex in videoClips {

    do {
        try videoCompositionTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, clipIndex.duration),
                                                  ofTrack: clipIndex.tracksWithMediaType(AVMediaTypeVideo)[0] ,
                                                  atTime: lastTime)
        lastTime = CMTimeAdd(lastTime, clipIndex.duration)
    } catch {
        print("Failed to insert track")
    }
}
print("VideoComposition Tracks: \(videoComposition.tracks.count)") // Shows multiple tracks

playerItem = AVPlayerItem(asset: videoComposition)
print("PlayerItem Duration: \(playerItem.duration.seconds)") // Shows the duration of all tracks together
print("PlayerItem Tracks: \(playerItem.tracks.count)") // Shows same number of tracks as the VideoComposition Track count

videoPlayer = AVPlayer(playerItem: playerItem)
playerLayer.player = videoPlayer
videoPlayer.volume = 0.0
videoPlayer.play()  // Does play all clips sequentially

编辑：我之前提到过，我仍然想知道如何在一个资产中播放多个曲目。这不是它的工作原理，我现在明白了。一个很好的资源：

https://developer.apple.com/library/mac/documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/04_MediaCapture.html