カスタム AVVideoCompositing クラスが期待どおりに動作しない 質問する

残り2つのクラスはここにあります。この投稿を短くするために、両方を1つのコードブロックにまとめます。

// Video Filter Composition Instruction Class - from what I gather,
// AVVideoCompositionInstruction is used only to pass values to
// the AVVideoCompositing class

class VideoFilterCompositionInstruction : AVMutableVideoCompositionInstruction{

    let trackID: CMPersistentTrackID
    let filters: ImageFilterGroup
    let context: CIContext


    // When I leave this line as-is, startVideoCompositionRequest: isn't called.
    // When commented out, startVideoCompositionRequest(request) is called, but there
    // are no valid CVPixelBuffers provided by request.sourceFrameByTrackID(below value)
    override var passthroughTrackID: CMPersistentTrackID{get{return self.trackID}}
    override var requiredSourceTrackIDs: [NSValue]{get{return []}}
    override var containsTweening: Bool{get{return false}}


    init(trackID: CMPersistentTrackID, filters: ImageFilterGroup, context: CIContext){
        self.trackID = trackID
        self.filters = filters
        self.context = context

        super.init()

        //self.timeRange = timeRange
        self.enablePostProcessing = true
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}


// My custom AVVideoCompositing class. This is where the problem lies -
// although I don't know if this is the root of the problem

class VideoFilterCompositor : NSObject, AVVideoCompositing{

    var requiredPixelBufferAttributesForRenderContext: [String : AnyObject] = [
        kCVPixelBufferPixelFormatTypeKey as String : NSNumber(unsignedInt: kCVPixelFormatType_32BGRA), // The video is in 32 BGRA
        kCVPixelBufferOpenGLESCompatibilityKey as String : NSNumber(bool: true),
        kCVPixelBufferOpenGLCompatibilityKey as String : NSNumber(bool: true)
    ]
    var sourcePixelBufferAttributes: [String : AnyObject]? = [
        kCVPixelBufferPixelFormatTypeKey as String : NSNumber(unsignedInt: kCVPixelFormatType_32BGRA),
        kCVPixelBufferOpenGLESCompatibilityKey as String : NSNumber(bool: true),
        kCVPixelBufferOpenGLCompatibilityKey as String : NSNumber(bool: true)
    ]

    let renderQueue = dispatch_queue_create("co.getblix.videofiltercompositor.renderingqueue", DISPATCH_QUEUE_SERIAL)

    override init(){
        super.init()
    }

    func startVideoCompositionRequest(request: AVAsynchronousVideoCompositionRequest){
       // This code block is never executed when the
       // passthroughTrackID variable is in the above class  

        autoreleasepool(){
            dispatch_async(self.renderQueue){
                guard let instruction = request.videoCompositionInstruction as? VideoFilterCompositionInstruction else{
                    request.finishWithError(NSError(domain: "getblix.co", code: 760, userInfo: nil))
                    return
                }
                guard let pixels = request.sourceFrameByTrackID(instruction.passthroughTrackID) else{
                    // This code block is executed when I comment out the
                    // passthroughTrackID variable in the above class            

                    request.finishWithError(NSError(domain: "getblix.co", code: 761, userInfo: nil))
                    return
                }
                // I have not been able to get the code to reach this point
                // This function is either not called, or the guard
                // statement above executes

                let image = CIImage(CVPixelBuffer: pixels)
                let filtered: CIImage = //apply the filter here

                let width = CVPixelBufferGetWidth(pixels)
                let height = CVPixelBufferGetHeight(pixels)
                let format = CVPixelBufferGetPixelFormatType(pixels)

                var newBuffer: CVPixelBuffer?
                CVPixelBufferCreate(kCFAllocatorDefault, width, height, format, nil, &newBuffer)

                if let buffer = newBuffer{
                    instruction.context.render(filtered, toCVPixelBuffer: buffer)
                    request.finishWithComposedVideoFrame(buffer)
                }
                else{
                    request.finishWithComposedVideoFrame(pixels)
                }
            }
        }
    }

    func renderContextChanged(newRenderContext: AVVideoCompositionRenderContext){
        // I don't have any code in this block
    }

    // This is interesting - this is called twice,
    // Once before startVideoCompositionRequest is called,
    // And once after. In the case when startVideoCompositionRequest
    // Is not called, this is simply called twice in a row
    func cancelAllPendingVideoCompositionRequests(){
        dispatch_barrier_async(self.renderQueue){
            print("Cancelled")
        }
    }
}