在AVFoundation中进行帧间视频压缩的方法

我创建了一个过程，该过程可以在我正在构建的应用程序中根据照片和图像的集合生成视频“幻灯片”。该过程正常运行，但是如果视频中包含的任何照片重复100到150帧不变，则会创建不必要的大文件。我已经包括了在AVFoundation中可以找到的任何压缩方式，其中大部分都应用了帧内技术，并试图在AVFoundation中找到有关帧间压缩的更多信息。不幸的是，我只能找到一些参考资料，而没有任何东西能让我正常工作。

我希望有人可以指引我正确的方向。视频生成器的代码包含在下面。我没有包含用于获取和准备单个框架的代码（以下称为self.getFrame（）），因为它似乎可以正常工作并且变得非常复杂，因为它可以处理照片，视频，添加标题框架以及进行淡入淡出过渡。对于重复的帧，它将返回带有帧图像的结构以及要包含的输出帧数的计数器。

        // Create a new AVAssetWriter Instance that will build the video

        assetWriter = createAssetWriter(path: filePathNew, size: videoSize!)
        guard assetWriter != nil else
        {
            print("Error converting images to video: AVAssetWriter not created.")
            inProcess = false
            return
        }

        let writerInput = assetWriter!.inputs.filter{ $0.mediaType == AVMediaTypeVideo }.first!

        let sourceBufferAttributes : [String : AnyObject] = [
            kCVPixelBufferPixelFormatTypeKey as String : Int(kCVPixelFormatType_32ARGB) as AnyObject,
            kCVPixelBufferWidthKey as String : videoSize!.width as AnyObject,
            kCVPixelBufferHeightKey as String : videoSize!.height as AnyObject,
            AVVideoMaxKeyFrameIntervalKey as String : 50 as AnyObject,
            AVVideoCompressionPropertiesKey as String : [
                AVVideoAverageBitRateKey: 725000,
                AVVideoProfileLevelKey: AVVideoProfileLevelH264Baseline30,
                ] as AnyObject
        ]

        let pixelBufferAdaptor = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: writerInput, sourcePixelBufferAttributes: sourceBufferAttributes)

        // Start the writing session

        assetWriter!.startWriting()

        assetWriter!.startSession(atSourceTime: kCMTimeZero)

        if (pixelBufferAdaptor.pixelBufferPool == nil) {
            print("Error converting images to video: pixelBufferPool nil after starting session")
            inProcess = false
            return
        }

        // -- Create queue for <requestMediaDataWhenReadyOnQueue>

        let mediaQueue = DispatchQueue(label: "mediaInputQueue")

        // Initialize run time values

        var presentationTime = kCMTimeZero
        var done = false
        var nextFrame: FramePack?                // The FramePack struct has the frame to output, noDisplays - the number of times that it will be output
                                                 // and an isLast flag that is true when it's the final frame

        writerInput.requestMediaDataWhenReady(on: mediaQueue, using: { () -> Void in    // Keeps invoking the block to get input until call markAsFinished

            nextFrame = self.getFrame()          // Get the next frame to be added to the output with its associated values
            let imageCGOut = nextFrame!.frame    // The frame to output
            if nextFrame!.isLast { done = true } // Identifies the last frame so can drop through to markAsFinished() below

            var frames = 0                       // Counts how often we've output this frame
            var waitCount = 0                    // Used to avoid an infinite loop if there's trouble with writer.Input

            while (frames < nextFrame!.noDisplays) && (waitCount < 1000000)  // Need to wait for writerInput to be ready - count deals with potential hung writer
            {
                waitCount += 1
                if waitCount == 1000000     // Have seen it go into 100s of thousands and succeed
                {
                    print("Exceeded waitCount limit while attempting to output slideshow frame.")
                    self.inProcess = false
                    return
                }

                if (writerInput.isReadyForMoreMediaData)
                {
                    waitCount = 0
                    frames += 1

                    autoreleasepool
                        {
                            if  let pixelBufferPool = pixelBufferAdaptor.pixelBufferPool
                            {
                                let pixelBufferPointer = UnsafeMutablePointer<CVPixelBuffer?>.allocate(capacity: 1)
                                let status: CVReturn = CVPixelBufferPoolCreatePixelBuffer(
                                    kCFAllocatorDefault,
                                    pixelBufferPool,
                                    pixelBufferPointer
                                )

                                if let pixelBuffer = pixelBufferPointer.pointee, status == 0
                                {
                                    CVPixelBufferLockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: CVOptionFlags(0)))
                                    let pixelData = CVPixelBufferGetBaseAddress(pixelBuffer)
                                    let rgbColorSpace = CGColorSpaceCreateDeviceRGB()

                                    // Set up a context for rendering using the PixelBuffer allocated above as the target

                                    let context = CGContext(
                                        data: pixelData,
                                        width: Int(self.videoWidth),
                                        height: Int(self.videoHeight),
                                        bitsPerComponent: 8,
                                        bytesPerRow: CVPixelBufferGetBytesPerRow(pixelBuffer),
                                        space: rgbColorSpace,
                                        bitmapInfo: CGImageAlphaInfo.premultipliedFirst.rawValue
                                    )

                                    // Draw the image into the PixelBuffer used for the context

                                    context?.draw(imageCGOut, in: CGRect(x: 0.0,y: 0.0,width: 1280, height: 720))

                                    // Append the image (frame) from the context pixelBuffer onto the video file

                                    _ = pixelBufferAdaptor.append(pixelBuffer, withPresentationTime: presentationTime)
                                    presentationTime = presentationTime + CMTimeMake(1, videoFPS)

                                    // We're done with the PixelBuffer, so unlock it

                                    CVPixelBufferUnlockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: CVOptionFlags(0)))
                                }

                                pixelBufferPointer.deinitialize()
                                pixelBufferPointer.deallocate(capacity: 1)

                            } else {
                                NSLog("Error: Failed to allocate pixel buffer from pool")
                            }
                    }
                }
            }

在此先感谢您的任何建议。