AVMutableVideoComposition stops video from rendering - ios

Question

I am trying to get a composition of 2 videos playing simultaneously in different positions based on this tutorial: https://abdulazeem.wordpress.com/2012/04/02/video-manipulation-in-ios-resizingmerging-and-overlapping-videos-in-ios/
Here is my code:
-(AVPlayer*)create{
// assets
AVAsset* videoAsset = [AVAsset assetWithURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:#"video_mov" ofType:#"mov"]]];
AVAsset* videoAsset2 = [AVAsset assetWithURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:#"video_mov" ofType:#"mov"]]];
// create a mutable composition and 2 tracks
AVMutableComposition* mutableComposition = [AVMutableComposition composition];
AVMutableCompositionTrack* videoTrack1 = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVMutableCompositionTrack* videoTrack2 = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
// add tracks from the video asset into the videoTrack1 (MutableCompositionTrack)
[videoTrack1 insertTimeRange: CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
atTime:kCMTimeZero
error:nil];
[videoTrack2 insertTimeRange: CMTimeRangeMake(kCMTimeZero, videoAsset2.duration)
ofTrack:[[videoAsset2 tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
atTime:kCMTimeZero
error:nil];
// Add audio tracks from the audio asset to our audioCompositionTrack
[audioCompositionTrack insertTimeRange: CMTimeRangeMake(kCMTimeZero, audioAsset.duration)
ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0]
atTime:kCMTimeZero
error:nil];
// Now create composition instructions for
AVMutableVideoCompositionInstruction * MainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
MainInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, videoAsset.duration);
// Track 1
AVMutableVideoCompositionLayerInstruction* FirstlayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack1];
CGAffineTransform Scale = videoTrack1.preferredTransform;
CGAffineTransform Move = CGAffineTransformMakeTranslation(300,200);
[FirstlayerInstruction setTransform:CGAffineTransformConcat(Scale,Move) atTime:kCMTimeZero];
// Track 2
AVMutableVideoCompositionLayerInstruction *SecondlayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack2];
CGAffineTransform SecondScale = videoTrack1.preferredTransform;
CGAffineTransform SecondMove = CGAffineTransformMakeTranslation(0,0);
[SecondlayerInstruction setTransform:CGAffineTransformConcat(SecondScale,SecondMove) atTime:kCMTimeZero];
//Now we add our 2 created AVMutableVideoCompositionLayerInstruction objects to our AVMutableVideoCompositionInstruction in form of an array.
MainInstruction.layerInstructions = [NSArray arrayWithObjects:FirstlayerInstruction,nil];
// now create a video composition with the instruction, and set our instructions
AVMutableVideoComposition* videoComposition = [AVMutableVideoComposition videoComposition];
videoComposition.instructions = [NSArray arrayWithObject:MainInstruction];
videoComposition.frameDuration = CMTimeMake(1, 30);
videoComposition.renderSize = mutableComposition.naturalSize;
// Create the player item
AVPlayerItem* avPlayerItem =[[AVPlayerItem alloc]initWithAsset:mutableComposition];
avPlayerItem.videoComposition = videoComposition;
// Create the player and return it
AVPlayer* avPlayer = [[AVPlayer alloc]initWithPlayerItem:avPlayerItem];
return avPlayer;
}
The video does not render.
If I remove the line:
avPlayerItem.videoComposition = videoComposition;
The video renders again, since it has no custom videoComposition set on it. Several other examples I have seen appear to be doing this in the same way.
I can only assume my transform data is incorrect, Although I have tried various different numbers.

Answer 1

Try to create immutable composition apple doesn't recommend to play mutable composition
AVComposition *immutableSnapshotOfMyComposition = [myMutableComposition copy];
// Create a player to inspect and play the composition.
AVPlayerItem *playerItemForSnapshottedComposition =
[[AVPlayerItem alloc] initWithAsset:immutableSnapshotOfMyComposition];