ios - AVMutableComposition - 只播放第一首轨道(Swift)

Question

我有一个 [AVAsset] 数组，我正在尝试将所有这些 Assets 组合成一个 Assets ，以便我可以无缝播放视频(我尝试使用 AVQueuePlayer，但它不会播放 Assets 无缝)。

下面是我目前所拥有的，但是当我尝试播放最终作品时，它只播放第一首轨道，即使它显示它有所有轨道并且总持续时间等于所有轨道加在一起。

我是否错过了一个步骤，即使看起来所有轨道都在合成中？如果 AVPlayerItem 有多个轨道，我可能需要以不同方式处理 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

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

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

这里是完整的、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:我之前提到我仍然想知道如何在一个 Assets 中播放多个轨道。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