循环 AVMutableCompositionTrack

我身上有两个音轨，我将它们相互组合起来，如下所示：

AVMutableComposition *composition = [[AVMutableComposition alloc] init];

AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack setPreferredVolume:1.0];
AVAsset *avAsset = [AVURLAsset URLAssetWithURL:originalContentURL options:nil];
AVAssetTrack *clipAudioTrack = [[avAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration) ofTrack:clipAudioTrack atTime:kCMTimeZero error:nil];

AVMutableCompositionTrack *compositionAudioTrack1 = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack1 setPreferredVolume:0.01];
NSString *soundOne1  =[[NSBundle mainBundle]pathForResource:@"jingle1" ofType:@"m4a"];
NSURL *url1 = [NSURL fileURLWithPath:soundOne1];
AVAsset *avAsset1 = [AVURLAsset URLAssetWithURL:url1 options:nil];
AVAssetTrack *clipAudioTrack1 = [[avAsset1 tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
[compositionAudioTrack1 insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration) ofTrack:clipAudioTrack1 atTime:kCMTimeZero error:nil];

正如你所看到的，第一个AVAsset是第二条轨道的基本长度，这意味着如果我有很长的第二条轨道，它将被剪切，这正是我想要的方式。

但是，我需要能够循环第二首曲目，以便如果first第一篇太长了，第二篇还在继续。我后来必须将生成的曲目保存在光盘上，这也是一个重要因素。

经过研究，我发现在 iOS 中没有方便的方法来实际循环曲目。解决方法之一是将第二个轨道插入AVMutableComposition一遍又一遍，但这对我来说听起来很奇怪。任何基于该主题的想法都会非常有用。

我认为它应该有效：

CMTime videoDuration = avAsset.duration;
if(CMTimeCompare(videoDuration, audioAsset.duration) == -1){
    [compositionAudioTrack1 insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration) ofTrack:clipAudioTrack1 atTime:kCMTimeZero error:nil];
}else if(CMTimeCompare(videoDuration, audioAsset.duration) == 1){
     CMTime currentTime = kCMTimeZero;
     while(YES){
           CMTime audioDuration = audioAsset.duration;
           CMTime totalDuration = CMTimeAdd(currentTime,audioDuration);
           if(CMTimeCompare(totalDuration, videoDuration)==1){
              audioDuration = CMTimeSubtract(totalDuration,videoDuration);

           }
           [compositionAudioTrack1 insertTimeRange:CMTimeRangeMake(kCMTimeZero, audioDuration) ofTrack:clipAudioTrack1 atTime:currentTime error:nil];
           currentTime = CMTimeAdd(currentTime, audioDuration);
           if(CMTimeCompare(currentTime, videoDuration) == 1 || CMTimeCompare(currentTime, videoDuration) == 0){
               break;
           }
     }
}