CATextLayer doesn't appear in an AVMutableComposition when running from a unit test

Question

EDIT: The strangest thing: it seems that when running this code from a full app everything works, but I was always running the creation of the movie from my unit tests, and only there it didn't work. Trying to figure out why is that...

I'm trying to combine video + audio + text using AVMutableComposition and export it to a new video.

My code is based on the AVEditDemo from WWDC '10

I added a purple background to the CATextLayer so I can know for a fact it is exported to the movie, but no text is shown... I tried playing with various fonts, position, color definitions, but nothing helped, so I decided to post the code here and see if anyone stumbled across something similar and can tell me what I'm missing.

Here's the code (self.audio and self.video are AVURLAssets):

CMTime exportDuration = self.audio.duration;

AVMutableComposition *composition = [[AVMutableComposition alloc] init];

AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVAssetTrack *videoTrack = [[self.video tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

// add the video in loop until the audio ends
CMTime currStartTime = kCMTimeZero;
while (CMTimeCompare(currStartTime, exportDuration) < 0) {
    CMTime timeRemaining = CMTimeSubtract(exportDuration, currStartTime);
    CMTime currLoopDuration = self.video.duration;

    if (CMTimeCompare(currLoopDuration, timeRemaining) > 0) {
        currLoopDuration = timeRemaining;
    }
    CMTimeRange currLoopTimeRange = CMTimeRangeMake(kCMTimeZero, currLoopDuration);

    [compositionVideoTrack insertTimeRange:currLoopTimeRange ofTrack:videoTrack
                                    atTime:currStartTime error:nil];

    currStartTime = CMTimeAdd(currStartTime, currLoopDuration);
}

AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

AVAssetTrack *audioTrack = [self.audio.tracks objectAtIndex:0];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, self.audio.duration) ofTrack:audioTrack atTime:kCMTimeZero error:nil];

AVMutableVideoComposition *videoComposition;

// the text layer part - THIS IS THE PART THAT DOESN'T WORK WELL
CALayer *animatedTitleLayer = [CALayer layer];
CATextLayer *titleLayer = [[CATextLayer alloc] init];
titleLayer.string = @"asdfasdf";
titleLayer.alignmentMode = kCAAlignmentCenter;
titleLayer.bounds = CGRectMake(0, 0, self.video.naturalSize.width / 2, self.video.naturalSize.height / 2);
titleLayer.opacity = 1.0;
titleLayer.backgroundColor = [UIColor purpleColor].CGColor;

[animatedTitleLayer addSublayer:titleLayer];
animatedTitleLayer.position = CGPointMake(self.video.naturalSize.width / 2.0, self.video.naturalSize.height / 2.0);

// build a Core Animation tree that contains both the animated title and the video.
CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];
parentLayer.frame = CGRectMake(0, 0, self.video.naturalSize.width, self.video.naturalSize.height);
videoLayer.frame = CGRectMake(0, 0, self.video.naturalSize.width, self.video.naturalSize.height);
[parentLayer addSublayer:videoLayer];
[parentLayer addSublayer:animatedTitleLayer];

videoComposition = [AVMutableVideoComposition videoComposition];
videoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];

AVMutableVideoCompositionInstruction *passThroughInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
passThroughInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, exportDuration);
AVMutableVideoCompositionLayerInstruction *passThroughLayer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTrack];

passThroughInstruction.layerInstructions = [NSArray arrayWithObject:passThroughLayer];
videoComposition.instructions = [NSArray arrayWithObject:passThroughInstruction];

videoComposition.frameDuration = CMTimeMake(1, 30);
videoComposition.renderSize = self.video.naturalSize;

AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetMediumQuality];

exportSession.videoComposition = videoComposition;
exportSession.outputURL = [NSURL fileURLWithPath:self.outputFilePath];
exportSession.outputFileType = AVFileTypeQuickTimeMovie;

[exportSession exportAsynchronouslyWithCompletionHandler:^() {
    // save the video ...
}];

Pursuer

I am not sure.. May be this could help..#7206320 – Osswald

Thanks, I'm doing something pretty much the same as what's mentioned there. If someone spots the critical difference between my code and the one in the relevant answer I'd be super grateful. – Pursuer

Have you tried setting the font size? – Fico

yes. as mentioned in the edit, this code successfully ran when I was running it with my full app, but when I created the video from a unit-test's code (using OCUnit), it didn't - still figuring out why is that. – Pursuer

Answer 1

Further investigation is needed, but AFAICT right now CATextLayer inside an AVMutableVideoComposition simply doesn't work from within a logic unit tests target, and this feature must be tested from a regular target.

Pursuer

Answer 2

I ran into the same issue in a different context. In my case, I had moved preparation of the AVMutableComposition to a background thread. Moving that part of preparation back to the main queue/thread made CATextLayer overlays work properly again.

This likely doesn't exactly apply to your unit testing context, but my guess is that CATextLayer/AVFoundation depend on some part of UIKit/AppKit being running/available (a drawing context? a current screen?) in that thread context, which might explain the failure we are both seeing.

Hautegaronne

Hi Adam do you know if it's possible to merge images and videos using AVMutableCompositionTracks (similar to how you merge video together), or do you need CALayers to incorporate images into a merged video. Question here: #34938362 – Stearns

Answer 3

I had the problem that almost everything rendered great, also images with CALayer and content set to CGImage. Except the CGTextLayer text, if I set a background color to CGTextLayer, a beginTime and duration that was perfectly rendered too - just the actual text didn't want to appear. That was all on the simulator, then I run it on the phone: And it was perfect.

Conclusion: The simulator renders nice videos... Until you use CATextLayer.

Standing

Answer 4

My problem was that I needed to set contentsGravity = kCAGravityBottomLeft -- otherwise my text was off the screen.

Concentrate