Invalid composition error (-11841) when trying to add CATextLayer to video

Question

I'm trying to add text over a video but no matter what I do I get invalid composition error (-11841). I have followed tutorials, read through threads and nothing stands out as being wrong. I am combining 3 videos, and an audio track and that works great. I'm trying to add the text for the duration of the first video clip (videoStartAsset).

Here is the code I'm using:

   var mainInstruction = AVMutableVideoCompositionInstruction()
    mainInstruction.timeRange = CMTimeRange(start: kCMTimeZero, duration: videoStartTimeRange.duration)

    var videoLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoCompositionTrack)
    var videoAssetTrack = videoStartAsset.tracksWithMediaType(AVMediaTypeVideo)[0] as AVAssetTrack

    videoLayerInstruction.setOpacity(0.0, atTime: videoStartTimeRange.duration)

    mainInstruction.layerInstructions = [videoLayerInstruction]

    var mainCompositionInst = AVMutableVideoComposition()
    var naturalSize = videoAssetTrack.naturalSize
    var renderWidth = naturalSize.width
    var renderHeight = naturalSize.height
    mainCompositionInst.renderScale = Float(UIScreen.mainScreen().scale)
    mainCompositionInst.renderSize = CGSize(width: 640.0, height: 480.0)
    mainCompositionInst.instructions = [mainInstruction]
    mainCompositionInst.frameDuration = CMTimeMake(1, 30)

    var nameTextLayer = CATextLayer()
    nameTextLayer.font = "FONT"
    nameTextLayer.fontSize = 100
    nameTextLayer.frame = CGRect(x: 0.0, y: 0.0, width: naturalSize.width, height: naturalSize.height)
    if let nameText = nameInputText?.label?.text {
        nameTextLayer.string = "TEXT"
    } else {
        nameTextLayer.string = "DEFAULT TEXT"
    }
    nameTextLayer.alignmentMode = kCAAlignmentCenter
    nameTextLayer.foregroundColor = UIColor.whiteColor().CGColor

    var overlayLayer = CALayer()
    overlayLayer.addSublayer(nameTextLayer)
    overlayLayer.frame = CGRect(x: 0.0, y: 0.0, width: naturalSize.width, height: naturalSize.height)
    overlayLayer.masksToBounds = true

    var parentLayer = CALayer()
    var videoLayer = CALayer()

    parentLayer.frame = CGRect(x: 0.0, y: 0.0, width: naturalSize.width, height: naturalSize.height)
    videoLayer.frame = CGRect(x: 0.0, y: 0.0, width: naturalSize.width, height: naturalSize.height)

    parentLayer.addSublayer(videoLayer)
    parentLayer.addSublayer(overlayLayer)

    mainCompositionInst.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer, inLayer: parentLayer)

Thanks.

Answer 1

Fixed my own problem; turns out the error was being thrown because of the following line:

mainInstruction.timeRange = CMTimeRange(start: kCMTimeZero, duration: videoStartTimeRange.duration)

This is because I am setting the timeRange to be the time range of the first video clip (where the text should be added), instead of the timeRange of the entire video (I am combining 3 videos into one, so I needed to set the timeRange to be the sum of all their durations).

Thank you Apple for the very descriptive error message. /sarcasm