如果视频持续时间长于音频持续时间，如何重复音频轨道

我正在使用AVMutableComposition混合音频和视频文件。 以下是我的代码：

enter code here
AVMutableComposition* mixComposition = [AVMutableComposition composition];

 NSString *bundleDirectory = [[NSBundle mainBundle] bundlePath];

 NSString *audio_inputFilePath = [bundleDirectory stringByAppendingPathComponent:@"xyz.mp3"];//audio of 35 seconds

 NSURL    *audio_inputFileUrl = [NSURL fileURLWithPath:audio_inputFilePath];

  NSURL    *video_inputFileUrl = [NSURL fileURLWithPath:videoOutputPath];

  NSString *outputFilePath = [documentsDirectory stringByAppendingPathComponent:@"video.mp4"];//video of 60 seconds

 NSURL    *outputFileUrl = [NSURL fileURLWithPath:outputFilePath];

 if ([[NSFileManager defaultManager] fileExistsAtPath:outputFilePath])
        [[NSFileManager defaultManager] removeItemAtPath:outputFilePath error:nil];

   CMTime nextClipStartTime = kCMTimeZero;

  AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:video_inputFileUrl options:nil];

 CMTimeRange video_timeRange = CMTimeRangeMake(kCMTimeZero,videoAsset.duration);

  AVMutableCompositionTrack *a_compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

 [a_compositionVideoTrack insertTimeRange:video_timeRange ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];

    AVURLAsset* audioAsset = [[AVURLAsset alloc]initWithURL:audio_inputFileUrl options:nil];
    enter code here
     CMTimeRange audio_timeRange = CMTimeRangeMake(kCMTimeZero, audioAsset.duration);
    enter code here
    AVMutableCompositionTrack *b_compositionAudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    [b_compositionAudioTrack insertTimeRange:audio_timeRange ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:nextClipStartTime error:nil];
    enter code here
    AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPreset640x480];

我面临的问题是我的音频文件持续时间比视频持续时间短。 所以我想做的是循环音频文件，直到视频结束。 就像我的视频是60秒，音频是35秒，所以音频应该重复25秒。

任何人都可以帮助我如何做到这一点。

---

方案1：创建一个新的CMTimeRange和insertTimeRange在AVMutableCompositionTrack

if (videoAsset.duration>audioAsset.duration)
{ 
    //new time range  
    CMTime duration = CMTimeMakeWithSeconds(CMTimeGetSeconds(videoAsset.duration)-CMTimeGetSeconds(audioAsset.duration), audioAsset.duration.timescale);
   if (CMTIME_IS_VALID(duration))
   {
    CMTimeRange video_timeRange2 = CMTimeRangeMake(audioAsset.duration,duration);
    //start from where left
    CMTime nextClipStartTime2 = audioAsset.duration;
    //add in AVMutableCompositionTrack
    [b_compositionVideoTrack insertTimeRange:video_timeRange2 ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime2 error:nil];
   }
   else
       NSLog(@"time is invalid");
}

注意 ：没有测试，但它应该工作。

编辑 ：

解决方案2 ：试试这个。 不要使用我的代码，并将下面的代码替换为你的代码

[b_compositionAudioTrack insertTimeRange:audio_timeRange ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:kCMTimeInvalid error:nil];

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