实时捕捉金属MTKView作为电影？

Question

从a中捕获帧的最有效方法是MTKView什么？如果可能的话,我想实时保存帧中的.mov文件.是否可以渲染到AVPlayer框架中？

它目前正在使用此代码绘制(基于@warrenm PerformanceShaders 项目):

func draw(in view: MTKView) {
     _ = inflightSemaphore.wait(timeout: DispatchTime.distantFuture)
             updateBuffers()

    let commandBuffer = commandQueue.makeCommandBuffer()

    commandBuffer.addCompletedHandler{ [weak self] commandBuffer in
        if let strongSelf = self {
            strongSelf.inflightSemaphore.signal()
        }
    }
   // Dispatch the current kernel to perform the selected image filter
    selectedKernel.encode(commandBuffer: commandBuffer,
        sourceTexture: kernelSourceTexture!,
        destinationTexture: kernelDestTexture!)

    if let renderPassDescriptor = view.currentRenderPassDescriptor, let currentDrawable = view.currentDrawable
    {
        let clearColor = MTLClearColor(red: 0, green: 0, blue: 0, alpha: 1)
        renderPassDescriptor.colorAttachments[0].clearColor = clearColor

        let renderEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor)
        renderEncoder.label = "Main pass"

        renderEncoder.pushDebugGroup("Draw textured square")
        renderEncoder.setFrontFacing(.counterClockwise)
        renderEncoder.setCullMode(.back)

        renderEncoder.setRenderPipelineState(pipelineState)
        renderEncoder.setVertexBuffer(vertexBuffer, offset: MBEVertexDataSize * bufferIndex, at: 0)
        renderEncoder.setVertexBuffer(uniformBuffer, offset: MBEUniformDataSize * bufferIndex , at: 1)
        renderEncoder.setFragmentTexture(kernelDestTexture, at: 0)
        renderEncoder.setFragmentSamplerState(sampler, at: 0)
        renderEncoder.drawPrimitives(type: .triangleStrip, vertexStart: 0, vertexCount: 4)

        renderEncoder.popDebugGroup()
        renderEncoder.endEncoding()

        commandBuffer.present(currentDrawable)
    }

    bufferIndex = (bufferIndex + 1) % MBEMaxInflightBuffers

    commandBuffer.commit()
 }

Answer 1

这是一个小类,它执行写出捕获Metal视图内容的电影文件的基本功能:

class MetalVideoRecorder {
    var isRecording = false
    var recordingStartTime = TimeInterval(0)

    private var assetWriter: AVAssetWriter
    private var assetWriterVideoInput: AVAssetWriterInput
    private var assetWriterPixelBufferInput: AVAssetWriterInputPixelBufferAdaptor

    init?(outputURL url: URL, size: CGSize) {
        do {
            assetWriter = try AVAssetWriter(outputURL: url, fileType: AVFileTypeAppleM4V)
        } catch {
            return nil
        }

        let outputSettings: [String: Any] = [ AVVideoCodecKey : AVVideoCodecH264,
            AVVideoWidthKey : size.width,
            AVVideoHeightKey : size.height ]

        assetWriterVideoInput = AVAssetWriterInput(mediaType: AVMediaTypeVideo, outputSettings: outputSettings)
        assetWriterVideoInput.expectsMediaDataInRealTime = true

        let sourcePixelBufferAttributes: [String: Any] = [
            kCVPixelBufferPixelFormatTypeKey as String : kCVPixelFormatType_32BGRA,
            kCVPixelBufferWidthKey as String : size.width,
            kCVPixelBufferHeightKey as String : size.height ]

        assetWriterPixelBufferInput = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: assetWriterVideoInput,
                                                                           sourcePixelBufferAttributes: sourcePixelBufferAttributes)

        assetWriter.add(assetWriterVideoInput)
    }

    func startRecording() {
        assetWriter.startWriting()
        assetWriter.startSession(atSourceTime: kCMTimeZero)

        recordingStartTime = CACurrentMediaTime()
        isRecording = true
    }

    func endRecording(_ completionHandler: @escaping () -> ()) {
        isRecording = false

        assetWriterVideoInput.markAsFinished()
        assetWriter.finishWriting(completionHandler: completionHandler)
    }

    func writeFrame(forTexture texture: MTLTexture) {
        if !isRecording {
            return
        }

        while !assetWriterVideoInput.isReadyForMoreMediaData {}

        guard let pixelBufferPool = assetWriterPixelBufferInput.pixelBufferPool else {
            print("Pixel buffer asset writer input did not have a pixel buffer pool available; cannot retrieve frame")
            return
        }

        var maybePixelBuffer: CVPixelBuffer? = nil
        let status  = CVPixelBufferPoolCreatePixelBuffer(nil, pixelBufferPool, &maybePixelBuffer)
        if status != kCVReturnSuccess {
            print("Could not get pixel buffer from asset writer input; dropping frame...")
            return
        }

        guard let pixelBuffer = maybePixelBuffer else { return }

        CVPixelBufferLockBaseAddress(pixelBuffer, [])
        let pixelBufferBytes = CVPixelBufferGetBaseAddress(pixelBuffer)!

        // Use the bytes per row value from the pixel buffer since its stride may be rounded up to be 16-byte aligned
        let bytesPerRow = CVPixelBufferGetBytesPerRow(pixelBuffer)
        let region = MTLRegionMake2D(0, 0, texture.width, texture.height)

        texture.getBytes(pixelBufferBytes, bytesPerRow: bytesPerRow, from: region, mipmapLevel: 0)

        let frameTime = CACurrentMediaTime() - recordingStartTime
        let presentationTime = CMTimeMakeWithSeconds(frameTime, 240)
        assetWriterPixelBufferInput.append(pixelBuffer, withPresentationTime: presentationTime)

        CVPixelBufferUnlockBaseAddress(pixelBuffer, [])
    }
}

在初始化其中一个并调用之后startRecording(),您可以将一个预定的处理程序添加到包含渲染命令和调用的命令缓冲区中writeFrame(在您结束编码之后,但在呈现drawable或提交缓冲区之前):

let texture = currentDrawable.texture
commandBuffer.addCompletedHandler { commandBuffer in
    self.recorder.writeFrame(forTexture: texture)
}

完成录制后,只需拨打电话endRecording,视频文件即可完成并关闭.

警告:

此类假定源纹理为默认格式.bgra8Unorm.如果不是,您将遭遇崩溃或腐败.如有必要,使用计算或片段着色器转换纹理,或使用"加速".

此类还假定纹理与视频帧的大小相同.如果不是这种情况(如果可绘制的大小发生变化,或者您的屏幕自动旋转),则输出将被破坏,您可能会看到崩溃.通过在应用程序需要时缩放或裁剪源纹理来缓解此问题.

Answer 2

升级到 Swift 5

import AVFoundation

class MetalVideoRecorder {
    var isRecording = false
    var recordingStartTime = TimeInterval(0)

    private var assetWriter: AVAssetWriter
    private var assetWriterVideoInput: AVAssetWriterInput
    private var assetWriterPixelBufferInput: AVAssetWriterInputPixelBufferAdaptor

    init?(outputURL url: URL, size: CGSize) {
        do {
          assetWriter = try AVAssetWriter(outputURL: url, fileType: AVFileType.m4v)
        } catch {
            return nil
        }

      let outputSettings: [String: Any] = [ AVVideoCodecKey : AVVideoCodecType.h264,
            AVVideoWidthKey : size.width,
            AVVideoHeightKey : size.height ]

      assetWriterVideoInput = AVAssetWriterInput(mediaType: AVMediaType.video, outputSettings: outputSettings)
        assetWriterVideoInput.expectsMediaDataInRealTime = true

        let sourcePixelBufferAttributes: [String: Any] = [
            kCVPixelBufferPixelFormatTypeKey as String : kCVPixelFormatType_32BGRA,
            kCVPixelBufferWidthKey as String : size.width,
            kCVPixelBufferHeightKey as String : size.height ]

        assetWriterPixelBufferInput = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: assetWriterVideoInput,
                                                                           sourcePixelBufferAttributes: sourcePixelBufferAttributes)

        assetWriter.add(assetWriterVideoInput)
    }

    func startRecording() {
        assetWriter.startWriting()
      assetWriter.startSession(atSourceTime: CMTime.zero)

        recordingStartTime = CACurrentMediaTime()
        isRecording = true
    }

    func endRecording(_ completionHandler: @escaping () -> ()) {
        isRecording = false

        assetWriterVideoInput.markAsFinished()
        assetWriter.finishWriting(completionHandler: completionHandler)
    }

    func writeFrame(forTexture texture: MTLTexture) {
        if !isRecording {
            return
        }

        while !assetWriterVideoInput.isReadyForMoreMediaData {}

        guard let pixelBufferPool = assetWriterPixelBufferInput.pixelBufferPool else {
            print("Pixel buffer asset writer input did not have a pixel buffer pool available; cannot retrieve frame")
            return
        }

        var maybePixelBuffer: CVPixelBuffer? = nil
        let status  = CVPixelBufferPoolCreatePixelBuffer(nil, pixelBufferPool, &maybePixelBuffer)
        if status != kCVReturnSuccess {
            print("Could not get pixel buffer from asset writer input; dropping frame...")
            return
        }

        guard let pixelBuffer = maybePixelBuffer else { return }

        CVPixelBufferLockBaseAddress(pixelBuffer, [])
        let pixelBufferBytes = CVPixelBufferGetBaseAddress(pixelBuffer)!

        // Use the bytes per row value from the pixel buffer since its stride may be rounded up to be 16-byte aligned
        let bytesPerRow = CVPixelBufferGetBytesPerRow(pixelBuffer)
        let region = MTLRegionMake2D(0, 0, texture.width, texture.height)

        texture.getBytes(pixelBufferBytes, bytesPerRow: bytesPerRow, from: region, mipmapLevel: 0)

        let frameTime = CACurrentMediaTime() - recordingStartTime
        let presentationTime = CMTimeMakeWithSeconds(frameTime, preferredTimescale:   240)
        assetWriterPixelBufferInput.append(pixelBuffer, withPresentationTime: presentationTime)

        CVPixelBufferUnlockBaseAddress(pixelBuffer, [])
    
        // You need to release memory allocated to pixelBuffer
        CVPixelBufferRelease(pixelBuffer)
    }
}

编辑：添加CVPixelBufferRelease(pixelBuffer)以避免内存泄漏。如果没有这个，在每一帧中新创建的 PixelBuffer 将保留在内存中，最终应用程序将为您提供所有可用的系统内存。