Ranges without video in AVMutableCompositionTrack and AVMutableVideoComposition issues

Question

I create a composition with several video clips, i also add some empty ranges where I show title screens with CoreAnimation.

|--Video1--|--NoVideo(AVsyncLayer)--|--Video2--|

Etc... Which all works fine, the problem comes when I start using: AVMutableVideoComposition, AVMutableVideoCompositionInstruction and AVMutableVideoCompositionLayerInstruction which I have to do to rotate videos properly.

|--Video1--|--NoVideo(AVsyncLayer)--|

Works fine in my AVPlayer, but if I instead do:

|--NoVideo(AVsyncLayer)--|--Video1--|

The application crashes the next time I push a new view controller, or pop the current view controller in my Navigation Controller stack. Sometimes with a memory warning sometimes without it, but according to instruments I only allocated 1.5Mb.

I've watched the Working With Media in AVFoundation from last years WWDC several times, and the only thing I can think of is that the comment

AVMutableVideoCompositionInstruction must not overlap or contain gaps.

Which it really doesn't. I have instructions for the full duration of the composition. But there are gaps in the AVMutableCompositionTrack (my video track) where I don't plan to show video, but only the CoreAnimation layer.

Have anyone else experienced similar issues?

insertEmptyTimeRange works for me in the middle of segments, but I've seen problems where the video ends in an empty segment of track - think title credits over black emptiness. Haven't found a solution yet. — Duane Fields
Duane, see my answer below, thats how we manage to get it to work — Erik

Duane Fields Duane Fields · Accepted Answer · 2012-10-09T14:36:16

Expanding on Erik's solution, here's what I did. I create a very brief black movie clip, and add this to the tail end of the empty time range. It seems to work fine, though I'd hope a more elegant solution exists. (Note that in my code TMAVCompositionTrack is just a wrapper that holds AVMutableCompositionTrack's for audio and video, along with some other things.

- (void)createEmptySpaceOnTrack:(TMAVCompositionTrack*)avtrack timeRange:(CMTimeRange)timeRangeOfShot {
        [avtrack.videoCompositionTrack insertEmptyTimeRange:timeRangeOfShot];
        [avtrack.audioCompositionTrack insertEmptyTimeRange:timeRangeOfShot];

        // there is a bug where emptyness is trimmed out, so put a brief burst of video blackness at the end of the "emptyness"
        NSURL* assetURL = [[NSBundle mainBundle] URLForResource:@"blackness" withExtension:@"mov"];
        AVAsset* asset = [AVURLAsset URLAssetWithURL:assetURL options:@{ AVURLAssetPreferPreciseDurationAndTimingKey:@(YES) }];
        AVAssetTrack *clipVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
        CMTimeRange timeRangeInAsset = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(0.01, 600));
        CMTime tailEnd = CMTimeSubtract(CMTimeRangeGetEnd(timeRangeOfShot), timeRangeInAsset.duration);
        [avtrack.videoCompositionTrack insertTimeRange:timeRangeInAsset ofTrack:clipVideoTrack atTime:tailEnd  error:nil];
    }

Ranges without video in AVMutableCompositionTrack and AVMutableVideoComposition issues

3 Answers