processing .mp4 file generates a black screen video with audio.

[han4wluc]

I am processing this video:

  NSURL *inputUrl = [NSURL fileURLWithPath:inputPath];
  AVURLAsset *inputUrlAsset = [AVURLAsset assetWithURL:inputUrl];

  NSURL *outputUrl = [NSURL fileURLWithPath:outputPath];
  
  SDAVAssetExportSession *encoder = [SDAVAssetExportSession.alloc initWithAsset:inputUrlAsset];
  encoder.outputFileType = AVFileTypeMPEG4;
  encoder.outputURL = outputUrl;
  //  1280x720
  encoder.videoSettings = @
  {
  AVVideoCodecKey: AVVideoCodecH264,
  AVVideoWidthKey: @720,
  AVVideoHeightKey: @1280,
  AVVideoCompressionPropertiesKey: @
    {
    AVVideoAverageBitRateKey: @512000,
    AVVideoProfileLevelKey: AVVideoProfileLevelH264High40,
    },
  };
  encoder.audioSettings = @
  {
  AVFormatIDKey: @(kAudioFormatMPEG4AAC),
  AVNumberOfChannelsKey: @2,
  AVSampleRateKey: @44100,
  AVEncoderBitRateKey: @96000,
  };
  
  [encoder exportAsynchronouslyWithCompletionHandler:^
  {
    if (encoder.status == AVAssetExportSessionStatusCompleted)
    {
      NSLog(@"Video export succeeded");
    }
    else if (encoder.status == AVAssetExportSessionStatusCancelled)
    {
      NSLog(@"Video export cancelled");
    }
    else
    {
      NSLog(@"Video export failed with error: %@ (%d)", encoder.error.localizedDescription, encoder.error.code);
    }
  }];

The output video is a black screen with the audio.
I am able to process .mov files without problem.
Does anyone know where the problem lies?

[newacct]

I encountered this with some video tracks whose preferredTransform had a rotation but which didn't have an appropriate translation to shift it back into view, for some unknown reason. The following seems to fix it:

After the line CGAffineTransform transform = videoTrack.preferredTransform; in -[SDAVAssetExportSession buildDefaultVideoComposition], add the following lines:

  CGRect rect = {{0, 0}, naturalSize};
  CGRect transformedRect = CGRectApplyAffineTransform(rect, transform);
  // transformedRect should have origin at 0 if correct; otherwise add offset to correct it
  transform.tx -= transformedRect.origin.x;
  transform.ty -= transformedRect.origin.y;

[Shebuka]

I was investigating the same problem with a video shared to our app from WhatsApp that produced a black video with audio. The buildDefaultVideoComposition method was one of the possible causes on my list and I've planned to debug into today. Now will try @newacct fix and report back.

[Shebuka]

It's working correctly now with @newacct fix.

I'm attaching the incriminated video file so you can test with it: WhatsApp Video 2018-01-18 at 17.48.32.mp4.zip

[JasonPrenger]

I was also encountering this issue and the fix by @newacct worked well.

[imdatceleste]

@newacct thanks, that helped me a lot