Estou criando um aplicativo baseado em vídeo, onde tenho que selecionar qualquer vídeo da galeria local e adicionar um texto usando CATextLayer sobre o vídeo. Para isso, estou usando o código abaixo:

- (void) createWatermark:(UIImage*)image video:(NSURL*)videoURL
{
    if (videoURL == nil)
        return;

    AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:videoURL options:nil];
    AVMutableComposition* mixComposition = [AVMutableComposition composition];

    AVMutableCompositionTrack* compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo  preferredTrackID:kCMPersistentTrackID_Invalid];

    AVAssetTrack* clipVideoTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
                                   ofTrack:clipVideoTrack
                                    atTime:kCMTimeZero error:nil];

    [compositionVideoTrack setPreferredTransform:[[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] preferredTransform]];

    //  create the layer with the watermark image
    CALayer* aLayer = [CALayer layer];
    aLayer.contents = (id)image.CGImage;
    aLayer.frame = CGRectMake(50, 100, image.size.width, image.size.height);
    aLayer.opacity = 0.9;

    //sorts the layer in proper order

    AVAssetTrack* videoTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    CGSize videoSize = [videoTrack naturalSize];
    CALayer *parentLayer = [CALayer layer];
    CALayer *videoLayer = [CALayer layer];
    parentLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);
    videoLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);
    [parentLayer addSublayer:videoLayer];
    [parentLayer addSublayer:aLayer];


    // create text Layer
    CATextLayer* titleLayer = [CATextLayer layer];
    titleLayer.backgroundColor = [UIColor clearColor].CGColor;
    titleLayer.string = @"Dummy text";
    titleLayer.font = CFBridgingRetain(@"Helvetica");
    titleLayer.fontSize = 28;
    titleLayer.shadowOpacity = 0.5;
    titleLayer.alignmentMode = kCAAlignmentCenter;
    titleLayer.frame = CGRectMake(0, 50, videoSize.width, videoSize.height / 6);

    [parentLayer addSublayer:titleLayer];

    //create the composition and add the instructions to insert the layer:

    AVMutableVideoComposition* videoComp = [AVMutableVideoComposition videoComposition];
    videoComp.renderSize = videoSize;
    videoComp.frameDuration = CMTimeMake(1, 30);
    videoComp.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];

    /// instruction
    AVMutableVideoCompositionInstruction* instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];

    instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [mixComposition duration]);
    AVAssetTrack* mixVideoTrack = [[mixComposition tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    AVMutableVideoCompositionLayerInstruction* layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:mixVideoTrack];
    instruction.layerInstructions = [NSArray arrayWithObject:layerInstruction];
    videoComp.instructions = [NSArray arrayWithObject: instruction];

    // export video

    _assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetMediumQuality];
    _assetExport.videoComposition = videoComp;

    NSLog (@"created exporter. supportedFileTypes: %@", _assetExport.supportedFileTypes);

    NSString* videoName = @"NewWatermarkedVideo.mov";

    NSString* exportPath = [NSTemporaryDirectory() stringByAppendingPathComponent:videoName];
    NSURL* exportUrl = [NSURL fileURLWithPath:exportPath];

    if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath])
        [[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil];

    _assetExport.outputFileType = AVFileTypeQuickTimeMovie;
    _assetExport.outputURL = exportUrl;
    _assetExport.shouldOptimizeForNetworkUse = YES;

    [_assetExport exportAsynchronouslyWithCompletionHandler:
     ^(void ) {

         //Final code here

         switch (_assetExport.status)
         {
             case AVAssetExportSessionStatusUnknown:
                 NSLog(@"Unknown");
                 break;
            case AVAssetExportSessionStatusWaiting:
                 NSLog(@"Waiting");
                 break;
             case AVAssetExportSessionStatusExporting:
                 NSLog(@"Exporting");
                 break;
             case AVAssetExportSessionStatusCompleted:
                 NSLog(@"Created new water mark image");
                 _playButton.hidden = NO;
                 break;
             case AVAssetExportSessionStatusFailed:
                 NSLog(@"Failed- %@", _assetExport.error);
                 break;
             case AVAssetExportSessionStatusCancelled:
                 NSLog(@"Cancelled");
                 break;
            }
     }
     ];   
}

Usando o código acima, posso definir um texto sobre o meu vídeo. Mas agora eu tenho que dar uma animação FadeIN / Fade Out no CATextLayer OU para exibir o texto em movimento no vídeo. Aconselhe-me por favor. Desde já, obrigado!