从MTKView
捕获帧的最有效方法是什么?如果可能的话,我想实时从框架中保存一个.mov文件。是否可以渲染到AVPlayer框架中?
当前正在使用此代码绘制(基于@warrenm PerformanceShaders project:]
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()
}
这是一小类,执行写出捕获金属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, [])
}
}
[初始化其中之一并调用startRecording()
后,可以将包含调度命令的处理程序添加到包含渲染命令的命令缓冲区中,并调用writeFrame
(在结束编码之后,但在呈现可绘制对象或提交缓冲区之前):] >
let texture = currentDrawable.texture commandBuffer.addCompletedHandler { commandBuffer in self.recorder.writeFrame(forTexture: texture) }
录制完成后,只需调用
endRecording
,视频文件将最终确定并关闭。
注意事项
:此类假定源纹理为默认格式.bgra8Unorm
。如果不是这样,您将崩溃或损坏。如有必要,请使用计算或片段着色器转换纹理,或使用“加速”。
此类还假定纹理的大小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更改,或者屏幕自动旋转),则输出将损坏,并且您可能会看到崩溃。通过根据应用程序的需要缩放或裁剪源纹理来缓解此问题。
升级到Swift 5