AvMutableComposition问题在最后有黑框

Question

我在iOS应用中使用AVCaptureConnection捕获视频。之后，我在视频中添加一些图片作为CALayers。一切工作正常，但在添加图像后，我在结果视频的最后得到了一个黑框。没有实际的音频/视频帧受到影响。对于音频，我提取它并更改它的音高，然后使用AVMutableComposition添加它。这是我正在使用的代码。请帮我解决我所做的错误，或者我需要添加其他内容。

cmp = [AVMutableComposition composition]; 

    AVMutableCompositionTrack *videoComposition = [cmp addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid]; 
    AVMutableCompositionTrack *audioComposition = [cmp addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid]; 
    AVAssetTrack *sourceVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]; 
    AVAssetTrack *sourceAudioTrack = [[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0]; 


    [videoComposition insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:sourceVideoTrack atTime:kCMTimeZero error:nil] ; 
    [audioComposition insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:sourceAudioTrack atTime:kCMTimeZero error:nil]; 

    animComp = [AVMutableVideoComposition videoComposition]; 
    animComp.renderSize = CGSizeMake(320, 320); 
    animComp.frameDuration = CMTimeMake(1,30); 
    animComp.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer]; 

    // to gather the audio part of the video 
    NSArray *tracksToDuck = [cmp tracksWithMediaType:AVMediaTypeAudio]; 
    NSMutableArray *trackMixArray = [NSMutableArray array]; 
    for (NSInteger i = 0; i < [tracksToDuck count]; i++) { 
     AVMutableAudioMixInputParameters *trackMix = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:[tracksToDuck objectAtIndex:i]]; 
     [trackMix setVolume:5 atTime:kCMTimeZero]; 
     [trackMixArray addObject:trackMix]; 
    } 
    audioMix = [AVMutableAudioMix audioMix]; 
    audioMix.inputParameters = trackMixArray; 

    AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction]; 
    instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [asset duration]); 
    AVMutableVideoCompositionLayerInstruction *layerVideoInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoComposition]; 

    [layerVideoInstruction setOpacity:1.0 atTime:kCMTimeZero]; 
    instruction.layerInstructions = [NSArray arrayWithObject:layerVideoInstruction] ; 
    animComp.instructions = [NSArray arrayWithObject:instruction]; 
    [self exportMovie:self]; 

这是我导出视频

-(IBAction) exportMovie:(id)sender{ 

    //successCheck = NO; 
    NSArray *docPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
    NSString *tempPath = [docPaths objectAtIndex:0]; 
    //NSLog(@"Temp Path: %@",tempPath); 

    NSString *fileName = [NSString stringWithFormat:@"%@/Final.MP4",tempPath]; 
    NSFileManager *fileManager = [NSFileManager defaultManager] ; 
    if([fileManager fileExistsAtPath:fileName ]){ 
     NSError *ferror = nil ; 
     [fileManager removeItemAtPath:fileName error:&ferror]; 
    } 

    NSURL *exportURL = [NSURL fileURLWithPath:fileName]; 

    AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:cmp presetName:AVAssetExportPresetMediumQuality] ; 
    exporter.outputURL = exportURL; 
    exporter.videoComposition = animComp; 
    //exporter.audioMix = audioMix; 
    exporter.outputFileType = AVFileTypeQuickTimeMovie; 

    [exporter exportAsynchronouslyWithCompletionHandler:^(void){ 
     switch (exporter.status) { 
      case AVAssetExportSessionStatusFailed:{ 
       NSLog(@"Fail"); 
       break; 
      } 
      case AVAssetExportSessionStatusCompleted:{ 
       NSLog(@"Success video"); 
           }); 
       break; 
      } 

      default: 
       break; 
     } 
      }]; 
    NSLog(@"outside"); 
} 

Answer 1

方法有给的时间范围内， 试着给时间范围略小于实际的时间（几纳秒少exportsession的属性）

Answer 2

感谢khushboo。我有同样的问题。 作为我的考验。只有10.7系统版本有这个问题。 10.8没有。 通过设置导出会话的时间范围解决了这个问题。