title: AvMutableComposition issues having black frame at the end
body: <p>I capturing a video using AVCaptureConnection in my iOS app. After that I add some images in the video as CALayers. Everything is working fine but I get a black frame at the very end of the resulting video after adding images. There is no frame of actual audio/video that has been affected in this. For audio I am extracting it and changing its pitch and then add it using AVMutableComposition. Here is the code that I am using. Please help me with what I am doing wrong or do I need to add something else.</p>
  
  <pre><code>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 &lt; [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];
  </code></pre>
  
  <p>This is my method for exporting the video</p>
  
  <pre><code>-(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:&amp;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");
  }
  </code></pre>