__Copy_helper_block_ error in AVFoundation

Question

I have a strange crash in a video processing application. It uses AVFoundation to work with video and audio, and GPUImage for filtering. I have never encountered this problem myself, but after its release on the App Store, it appeared in Crashlytics quite often. Here is the crash log:

 Thread : Crashed: AVPlayerItemOutput queue 0 libobjc.A.dylib 0x00000001986f80b4 objc_retain + 20 1 libsystem_blocks.dylib 0x0000000198d79bf8 _Block_object_assign + 320 2 AVFoundation 0x0000000186895a34 __copy_helper_block_171 + 36 3 libsystem_blocks.dylib 0x0000000198d79738 _Block_copy_internal + 384 4 libdispatch.dylib 0x0000000198d252fc _dispatch_Block_copy + 36 5 libdispatch.dylib 0x0000000198d2685c dispatch_async + 68 6 AVFoundation 0x00000001868959ac -[AVPlayerItemVideoOutput _dispatchOutputSequenceWasFlushed] + 112 7 libdispatch.dylib 0x0000000198d2536c _dispatch_client_callout + 16 8 libdispatch.dylib 0x0000000198d2e6e8 _dispatch_barrier_sync_f_invoke + 76 9 AVFoundation 0x00000001868940a8 AVPlayerItemVideoOutput_figVCSequentialAvailable + 196 10 MediaToolbox 0x000000018a3c16f8 FigVisualContextImageAvailableSequential + 108 11 MediaToolbox 0x000000018a348ce8 itemremote_postNotificationWithPayload + 3996 12 MediaToolbox 0x000000018a342d60 FigPlayerRemoteCallbacksServer_SendNotifyPing + 924 13 MediaToolbox 0x000000018a342998 _XSendNotifyPing + 60 14 MediaToolbox 0x000000018a33f0d4 figmoviecallbacks_server + 112 15 MediaToolbox 0x000000018a33f018 fpr_ClientPortCallBack + 208 16 CoreFoundation 0x0000000187f44ce0 __CFMachPortPerform + 180 17 CoreFoundation 0x0000000187f598fc __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 56 18 CoreFoundation 0x0000000187f5985c __CFRunLoopDoSource1 + 436 19 CoreFoundation 0x0000000187f577dc __CFRunLoopRun + 1640 20 CoreFoundation 0x0000000187e851f4 CFRunLoopRunSpecific + 396 21 GraphicsServices 0x00000001910135a4 GSEventRunModal + 168 22 UIKit 0x000000018c7b6784 UIApplicationMain + 1488 23 MerryVideoEditor 0x000000010024b804 main (main.m:16) 24 libdyld.dylib 0x0000000198d4ea08 start + 4 

This is how I connect AVFoundation to GPUImage :

 class ProjectEditorViewController: UIViewController { private var videoPlayerView = VideoPlayerView() private var movieFile: GPUImageMovie! private var currentComposition: AVComposition! //...and other properties } // MARK: - Filtering & Playback extension ProjectEditorViewController{ func updatePlayer() { currentFilter.removeAllTargets() movieFile?.removeAllTargets() movieFile?.endProcessing() let time = self.videoPlayerView.player?.currentItem.currentTime() ?? kCMTimeZero let (composition, audioMix) = compositionBuilder.buildCompositionFromTimeLine(timeLine) videoPlayerView.setAsset(composition) videoPlayerView.playerItem.audioMix = audioMix movieFile = GPUImageMovie(playerItem: videoPlayerView.player.currentItem) currentFilter.applyFromOutput(movieFile, toInput: gpuPlayerView) movieFile.startProcessing() addSyncLayerIfNeededForComposition(composition) videoPlayerView.player.seekToTime(time, toleranceBefore: kPlayerToleranceSeekTime, toleranceAfter: kPlayerToleranceSeekTime) currentComposition = composition } func updatePlayerFilter(){ if movieFile != nil{ movieFile.removeAllTargets() currentFilter.applyFromOutput(movieFile, toInput: gpuPlayerView) if(!videoPlayerView.isPlaying) { movieFile.startProcessing() } addSyncLayerIfNeededForComposition(currentComposition) }else{ updatePlayer() } } } 

Any ideas what is wrong with my code? Any questions, comments, tips and answers are highly appreciated.

Answer 1

This is a problem in GPUImageMovie - when an instance adds itself as an AVPlayerItemVideoOutput delegate: [playerItemOutput setDelegate:self queue:videoProcessingQueue] , playerItemOutput does not release the delegate when the GPUImageMovie instance GPUImageMovie released. This later leads to a method call from the freed object (outputSequenceWasFlushed:) , and you get a failure. This was found using the NSZombie detector, and I fixed it by adding it to the GPUImageMovie dealloc method: [playerItemOutput setDelegate:nil queue:nil];

Good luck, Nikita;)

Answer 2

Wild hunch: some smartass broke something in avfoundation in 8.x For some reason I can "just work" in 7.x If my theory is swinging, bugreporter is a way to handle this (they will immediately start to ignore the new bugreport)

Answer 3

I agree with Igor, but setting the playerItemOutput delegate to nil did not help me. Therefore I added

 runSynchronouslyOnVideoProcessingQueue(^{ [playerItemOutput setDelegate: nil queue: nil]; [_playerItem removeOutput: playerItemOutput]; playerItemOutput = nil; }); 

in endProcessing after invalidating displayLink .

Hope this helps.