IPhone avcomposition问题

Question

我正在尝试创建一个视频，显示两个视频一个接一个地使用在iphone上的avcomposition。此代码可以工作，但是在新创建的视频的整个持续时间内，我只能看到其中一个视频

- (void) startEdit{

 AVMutableComposition* mixComposition = [AVMutableComposition composition];

 NSString* a_inputFileName = @"export.mov";
 NSString* a_inputFilePath = [NSTemporaryDirectory() stringByAppendingPathComponent:a_inputFileName];
 NSURL*    a_inputFileUrl = [NSURL fileURLWithPath:a_inputFilePath];

 NSString* b_inputFileName = @"output.mov";
 NSString* b_inputFilePath = [NSTemporaryDirectory() stringByAppendingPathComponent:b_inputFileName];
 NSURL*    b_inputFileUrl = [NSURL fileURLWithPath:b_inputFilePath];

 NSString* outputFileName = @"outputFile.mov";
 NSString* outputFilePath = [NSTemporaryDirectory() stringByAppendingPathComponent:outputFileName];
 NSURL*    outputFileUrl = [NSURL fileURLWithPath:outputFilePath];

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



 CMTime nextClipStartTime = kCMTimeZero;

 AVURLAsset* a_videoAsset = [[AVURLAsset alloc]initWithURL:a_inputFileUrl options:nil];
 CMTimeRange a_timeRange = CMTimeRangeMake(kCMTimeZero,a_videoAsset.duration);
 AVMutableCompositionTrack *a_compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
 [a_compositionVideoTrack insertTimeRange:a_timeRange ofTrack:[[a_videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];

 nextClipStartTime = CMTimeAdd(nextClipStartTime, a_timeRange.duration);

 AVURLAsset* b_videoAsset = [[AVURLAsset alloc]initWithURL:b_inputFileUrl options:nil];
 CMTimeRange b_timeRange = CMTimeRangeMake(kCMTimeZero, b_videoAsset.duration);
 AVMutableCompositionTrack *b_compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
    [b_compositionVideoTrack insertTimeRange:b_timeRange ofTrack:[[b_videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];



 AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetLowQuality];   
 _assetExport.outputFileType = @"com.apple.quicktime-movie";
 _assetExport.outputURL = outputFileUrl;

 [_assetExport exportAsynchronouslyWithCompletionHandler:
  ^(void ) {
   [self saveVideoToAlbum:outputFilePath]; 
  }       
  ];

}


- (void) saveVideoToAlbum:(NSString*)path{
 if(UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(path)){
  UISaveVideoAtPathToSavedPhotosAlbum (path, self, @selector(video:didFinishSavingWithError: contextInfo:), nil);
 }
}

- (void) video: (NSString *) videoPath didFinishSavingWithError: (NSError *) error contextInfo: (void *) contextInfo {
 NSLog(@"Finished saving video with error: %@", error);
} 

我已经发布了整个代码，因为它可能会对其他人有所帮助。

不应该

nextClipStartTime = CMTimeAdd(nextClipStartTime, a_timeRange.duration);

[b_compositionVideoTrack insertTimeRange:b_timeRange ofTrack:[[b_videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];

将第二个视频添加到第一个视频的末尾

干杯

Answer 1

我想通了。应该只有一个AVMutableCompositionTrack。

如下所示：

CMTime nextClipStartTime = kCMTimeZero;

    AVURLAsset* a_videoAsset = [[AVURLAsset alloc]initWithURL:a_inputFileUrl options:nil];
    CMTimeRange a_timeRange = CMTimeRangeMake(kCMTimeZero,a_videoAsset.duration);
    AVMutableCompositionTrack *a_compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
    [a_compositionVideoTrack insertTimeRange:a_timeRange ofTrack:[[a_videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];

    nextClipStartTime = CMTimeAdd(nextClipStartTime, a_timeRange.duration);

    AVURLAsset* b_videoAsset = [[AVURLAsset alloc]initWithURL:b_inputFileUrl options:nil];
    CMTimeRange b_timeRange = CMTimeRangeMake(kCMTimeZero, b_videoAsset.duration);
    [a_compositionVideoTrack insertTimeRange:b_timeRange ofTrack:[[b_videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];

Answer 2

我还没有发现缺陷，但我确实有几个建议：

首先，捕获insertTimeRange和所有其他机会中的错误，并对其进行检查。

其次，对于简单的添加视频的情况，你可以使用AVMutableComposition，而不会有太多的音轨混乱。对从文件中初始化的AVAssets使用"insertTimeRange:ofAsset:atTime:error:“，你会大大简化你的代码。如果你需要做一些更复杂的事情，比如交叉渐变，你还需要使用视频合成和音频混合，在这一点上，你可以处理复杂的曲目。