CAKeyframeAnimation not animating CATextLayer when exporting video - ios7

Question

I have an application that I am attempting to put a timestamp on a video. To do this I am using AVFoundation and Core Animation to place a CATextLayer over the video layer. If I place text into the CATextLayer's string property, the string is properly displayed in the exported video. If I then add the animation to the CATextLayer the text never changes. I figure I've overlooked something, but I can find what it is.
Thank you in advance for any help.
Here is a code example.
AVMutableComposition *composition = [AVMutableComposition composition];
AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
videoComposition.frameDuration = CMTimeMake(1, 30);
AVMutableCompositionTrack *videoCompositionTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVMutableAudioMix *audioMix = [AVMutableAudioMix audioMix];
AVMutableCompositionTrack *audioCompositionTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
NSDictionary *assetOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey];
AVAsset *asset = [[AVURLAsset alloc] initWithURL:myUrl options:assetOptions];
AVAssetTrack *audioAssetTrack = [[asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
[audioCompositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:audioAssetTrack atTime:kCMTimeZero error:nil];
AVAssetTrack *videoAssetTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
[videoCompositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:videoAssetTrack atTime:kCMTimeZero error:nil];
videoComposition.renderSize = videoCompositionTrack.naturalSize;
AVMutableVideoCompositionInstruction *videoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
videoCompositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, composition.duration);
AVMutableVideoCompositionLayerInstruction *videoCompositionLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoCompositionTrack];
[videoCompositionLayerInstruction setOpacity:1.0f atTime:kCMTimeZero];
videoCompositionInstruction.layerInstructions = #[videoCompositionLayerInstruction];
videoComposition.instructions = #[videoCompositionInstruction];
CALayer *parentLayer = [CALayer layer];
parentLayer.frame = CGRectMake(0.0f, 0.0f, videoComposition.renderSize.width, videoComposition.renderSize.height);
CALayer *videoLayer = [CALayer layer];
videoLayer.frame = CGRectMake(0.0f, 0.0f, videoComposition.renderSize.width, videoComposition.renderSize.height);
[parentLayer addSublayer:videoLayer];
CATextLayer *textLayer = [CATextLayer layer];
textLayer.font = (__bridge CFTypeRef)([UIFont fontWithName:#"Helvetica Neue" size:45.0f]);
textLayer.fontSize = 45.0f;
textLayer.foregroundColor = [UIColor colorWithRed:1.0f green:1.0f blue:1.0f alpha:1.0f].CGColor;
textLayer.shadowColor = [UIColor colorWithRed:0.0f green:0.0f blue:0.0f alpha:1.0f].CGColor;
textLayer.shadowOffset = CGSizeMake(0.0f, 0.0f);
textLayer.shadowOpacity = 1.0f;
textLayer.shadowRadius = 4.0f;
textLayer.alignmentMode = kCAAlignmentCenter;
textLayer.truncationMode = kCATruncationNone;
CAKeyframeAnimation *keyFrameAnimation = [CAKeyframeAnimation animationWithKeyPath:#"string"];
// Step 8: Set the animation values to the object.
keyFrameAnimation.calculationMode = kCAAnimationLinear;
keyFrameAnimation.values = #[#"12:00:00", #"12:00:01", #"12:00:02", #"12:00:03",
#"12:00:04", #"12:00:05", #"12:00:06", #"12:00:07",
#"12:00:08", #"12:00:09"];
keyFrameAnimation.keyTimes = #[[NSNumber numberWithFloat:0.0f], [NSNumber numberWithFloat:0.1f],
[NSNumber numberWithFloat:0.2f], [NSNumber numberWithFloat:0.3f],
[NSNumber numberWithFloat:0.4f], [NSNumber numberWithFloat:0.5f],
[NSNumber numberWithFloat:0.6f], [NSNumber numberWithFloat:0.7f],
[NSNumber numberWithFloat:0.8f], [NSNumber numberWithFloat:0.9f]];
keyFrameAnimation.beginTime = AVCoreAnimationBeginTimeAtZero;
keyFrameAnimation.duration = CMTimeGetSeconds(composition.duration);
keyFrameAnimation.removedOnCompletion = YES;
[textLayer addAnimation:keyFrameAnimation forKey:#"string"];
textLayer.frame = CGRectMake(0.0f, 20.0f, videoComposition.renderSize.width, 55.0f);
[parentLayer addSublayer:textLayer];
videoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];
AVAssetExportSession *exportSession = [AVAssetExportSession exportSessionWithAsset:composition presetName:AVAssetExportPreset1920x1080];
exportSession.videoComposition = videoComposition;
exportSession.audioMix = audioMix;
exportSession.outputFileType = [exportSession.supportedFileTypes objectAtIndex:0];
exportSession.outputURL = mySaveUrl;
[exportSession exportAsynchronouslyWithCompletionHandler:^{
self.delegate = nil;
switch (exportSession.status) {
case AVAssetExportSessionStatusCancelled:
NSLog(#"Export session cancelled.");
break;
case AVAssetExportSessionStatusCompleted:
NSLog(#"Export session completed.");
break;
case AVAssetExportSessionStatusFailed:
NSLog(#"Export session failed.");
break;
case AVAssetExportSessionStatusUnknown:
NSLog(#"Export session unknown status.");
break;
case AVAssetExportSessionStatusWaiting:
NSLog(#"Export session waiting.");
break;
default:
break;
}
NSError *error = exportSession.error;
if (error != nil) {
NSLog(#"An error ocurred while exporting. Error: %#: %#", error.localizedDescription, error.localizedFailureReason);
}
}];

Answer 1

I stay in contact with apple support and told me that it's a bug in his SDK. They are trying to fix the issue.
Also I open an incident in apple bug reporter, If you are apple developer, I recommend you open a new one to do more pressure over this incident.
https://bugreport.apple.com/logon
Best regards.

Answer 2

Finally I fond a solution in CATextLayer and animation. It's probably that it's not the best solution but at least it works fine.
To fix the issue we ought to pass NSString to UIImage or CALayer and then put all this images (CGImage) in NSMutableArray and load this mutable array in CAKeyAnimation and do the modification of contents variable
-(UIImage *)imageFromText:(NSString *)text
{
UIGraphicsBeginImageContextWithOptions(sizeImageFromText,NO,0.0);//Better resolution (antialiasing)
//UIGraphicsBeginImageContext(sizeImageFromText); // iOS is < 4.0
[text drawInRect:aRectangleImageFromText withAttributes:attributesImageFromText];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
Adding images to NSMutableArray
[NSMutableArrayAux addObject:(__bridge id)[self imageFromText:#"Hello"].CGImage];
Set CAKeyAnimation to modify contents of image (change image)
CAKeyframeAnimation *overlay = [CAKeyframeAnimation animationWithKeyPath:#"contents"];
overlay.values = [[NSArray alloc] initWithArray:NSMutableArrayAux];
It works really fine, but it takes 1 or 2 seconds to 5000 or 6000 images in array, and also with 15000/16000 images when you export your video it crash with a overflow error. This is another bug in framework.
As you know, this is a issue in framework, and this is a solution at least until apple fix CATextLayer and animated issue, also I give this solution to apple too.