I am trying to change the composition of a video composition (i.e. converting its composite frames) during playback. It seems that sometimes this works, and the video composition smoothly switches to a new set of transformations, but in other cases it simply freezes and stays with the current transformations. An AVPlayer instance does not have a status code, and there are no errors on the player or game element.
Has anyone experienced this before? Any suggestions on why this is happening or how to get around it will be appreciated.
Below is the code. An important bit is "playerItem.videoComposition = videoComposition", which starts here when you click on the video (for testing purposes).
Another solution to this problem would be to display the video on separate layers, but it is important that the videos are synchronized, so composition seems to be the only way to achieve this.
@implementation VideoView { CGSize _videoSize; CMTimeRange _videoFullRange; AVMutableCompositionTrack * _compositionTrackVideoA; AVMutableCompositionTrack * _compositionTrackVideoB; } + (Class)layerClass { return [AVPlayerLayer class]; } - (id)initWithFrame:(CGRect)frame { self = [super initWithFrame:frame]; if ( self ) { NSString * videoAPath = [[NSBundle mainBundle] pathForResource:@"cam09v2" ofType:@"mp4"]; NSString * videoBPath = [[NSBundle mainBundle] pathForResource:@"cam10v2_b" ofType:@"mp4"]; AVURLAsset * videoAAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:videoAPath] options:nil]; AVURLAsset * videoBAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:videoBPath] options:nil]; AVAssetTrack * videoATrack = [[videoAAsset tracksWithMediaType:AVMediaTypeVideo] lastObject]; AVAssetTrack * videoBTrack = [[videoBAsset tracksWithMediaType:AVMediaTypeVideo] lastObject]; AVAssetTrack * audioTrack = [[videoAAsset tracksWithMediaType:AVMediaTypeAudio] lastObject]; _videoSize = [videoATrack naturalSize]; CMTime videoDuration = videoAAsset.duration; _videoFullRange = CMTimeRangeMake(kCMTimeZero, videoDuration); AVMutableComposition *composition = [AVMutableComposition composition]; AVMutableCompositionTrack * compositionTrackVideoA = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid]; AVMutableCompositionTrack * compositionTrackVideoB = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid]; AVMutableCompositionTrack * compositionTrackAudio = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid]; compositionTrackVideoA.preferredTransform = videoATrack.preferredTransform; NSError * error = nil; if ( ! [compositionTrackVideoA insertTimeRange:_videoFullRange ofTrack:videoATrack atTime:kCMTimeZero error:&error] ) NSLog(@"%@", error); if ( ! [compositionTrackVideoB insertTimeRange:_videoFullRange ofTrack:videoBTrack atTime:kCMTimeZero error:&error] ) NSLog(@"%@", error); if ( ! [compositionTrackAudio insertTimeRange:_videoFullRange ofTrack:audioTrack atTime:kCMTimeZero error:&error] ) NSLog(@"%@", error); _compositionTrackVideoA = [compositionTrackVideoA copy]; _compositionTrackVideoB = [compositionTrackVideoB copy]; AVPlayerItem * playerItem = [AVPlayerItem playerItemWithAsset:composition]; AVPlayer * player = [AVPlayer playerWithPlayerItem:playerItem]; [(AVPlayerLayer *)self.layer setPlayer:player]; [player play]; [player addObserver:self forKeyPath:@"status" options:0 context:0]; [self updateCompositionForPlayerItem:playerItem]; UITapGestureRecognizer * tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(didTap:)]; [self addGestureRecognizer:tapGesture]; } return self; } - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { if ( [keyPath isEqualToString:@"status"] ) NSLog(@"STATUS %d", ((AVPlayer *)object).status ); } - (void)updateCompositionForPlayerItem:(AVPlayerItem *)playerItem { AVMutableVideoComposition * videoComposition = [AVMutableVideoComposition videoComposition]; AVMutableVideoCompositionInstruction *videoInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction]; videoInstruction.enablePostProcessing = NO; videoInstruction.timeRange = _videoFullRange; AVMutableVideoCompositionLayerInstruction * layerInstructionA = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:_compositionTrackVideoA]; CGAffineTransform transformA = CGAffineTransformMakeScale(0.5, 0.5); [layerInstructionA setTransform:transformA atTime:kCMTimeZero]; AVMutableVideoCompositionLayerInstruction * layerInstructionB = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:_compositionTrackVideoB]; CGAffineTransform transformB = CGAffineTransformMakeScale(0.5, 0.5); static int i = 0; transformB = CGAffineTransformTranslate(transformB, (i++ % 2 == 0) ? _videoSize.width : 0, _videoSize.height); [layerInstructionB setTransform:transformB atTime:kCMTimeZero]; videoInstruction.layerInstructions = [NSArray arrayWithObjects:layerInstructionA, layerInstructionB, nil]; videoComposition.instructions = [NSArray arrayWithObject:videoInstruction]; videoComposition.frameDuration = CMTimeMake(1, 30);
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