如何在AVCaptureSession中为每个视频帧应用滤镜？

Question

我正在编写一个应用程序，需要对使用AVCaptureSession捕获的视频应用过滤器。筛选后的输出会写入输出文件。我目前使用CIFilter和CIImage来过滤每个视频帧。

以下是代码:

func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!) {
    ...
    let pixelBuffer = CMSampleBufferGetImageBuffer(samples)!
    let options = [kCVPixelBufferPixelFormatTypeKey as String : kCVPixelFormatType_420YpCbCr8BiPlanarFullRange]
    let cameraImage = CIImage(cvImageBuffer: pixelBuffer, options: options)
    let filter = CIFilter(name: "CIGaussianBlur")!
    filter.setValue((70.0), forKey: kCIInputRadiusKey)
    filter.setValue(cameraImage, forKey: kCIInputImageKey)
    let result = filter.outputImage!
    var pixBuffer:CVPixelBuffer? = nil;
    let fmt = CVPixelBufferGetPixelFormatType(pixelBuffer)
    CVPixelBufferCreate(kCFAllocatorSystemDefault,
                        CVPixelBufferGetWidth(pixelBuffer),
                        CVPixelBufferGetHeight(pixelBuffer),
                        fmt,
                        CVBufferGetAttachments(pixelBuffer, .shouldPropagate),
                        &pixBuffer);

    CVBufferPropagateAttachments(pixelBuffer, pixBuffer!)
    let eaglContext = EAGLContext(api: EAGLRenderingAPI.openGLES3)!
    eaglContext.isMultiThreaded = true
    let contextOptions = [kCIContextWorkingColorSpace : NSNull(), kCIContextOutputColorSpace: NSNull()]
    let context = CIContext(eaglContext: eaglContext, options: contextOptions)
    CVPixelBufferLockBaseAddress( pixBuffer!, CVPixelBufferLockFlags(rawValue: 0))
    context.render(result, to: pixBuffer!)
    CVPixelBufferUnlockBaseAddress( pixBuffer!, CVPixelBufferLockFlags(rawValue: 0))
    var timeInfo = CMSampleTimingInfo(duration: sampleBuffer.duration,
                                      presentationTimeStamp: sampleBuffer.presentationTimeStamp,
                                      decodeTimeStamp: sampleBuffer.decodeTimeStamp)
    var sampleBuf:CMSampleBuffer? = nil;
    CMSampleBufferCreateReadyWithImageBuffer(kCFAllocatorDefault,
                                             pixBuffer!,
                                             samples.formatDescription!,
                                             &timeInfo,
                                             &sampleBuf)

    // write to video file
    let ret = assetWriterInput.append(sampleBuf!)
    ...
}

AVAssetWriterInput.append返回的始终是false。我在这里做错了什么？此外，我使用的方法非常低效。沿途创建了一些临时副本。是否可以就地完成？

- crab oz

---

你有没有改动sampleBuffer的代码呢？ - Nikhil Manapure

目前我没有修改sampleBuffer。不过，如果可以的话，那就太好了。这将使我无需为过滤输出创建新缓冲区。 - crab oz

看看这个链接。它说我们不能编辑它。只需使用那里介绍的方法查看错误即可。 - Nikhil Manapure

Answer 1

我使用了基本相同的代码，遇到了相同的问题。后来发现渲染用的像素缓冲区有问题。append(sampleBuffer:)一直返回false，assetWriter.error报错信息为:

Error Domain=AVFoundationErrorDomain Code=-11800 "操作无法完成" UserInfo={NSUnderlyingError=0x17024ba30 {Error Domain=NSOSStatusErrorDomain Code=-12780 "(null)"}, NSLocalizedFailureReason=未知错误(-12780), NSLocalizedDescription=操作无法完成}

有人表示这是一个bug（详见这里），已经提交了 https://bugreport.apple.com/web/?problemID=34574848。

但出乎意料的是，当使用原始像素缓冲区进行渲染时问题消失了。请参见以下代码:

let sourcePixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
let sourceImage = CIImage(cvImageBuffer: sourcePixelBuffer)
let filter = CIFilter(name: "CIGaussianBlur", withInputParameters: [kCIInputImageKey: sourceImage])!
let filteredImage = filter.outputImage!

var pixelBuffer: CVPixelBuffer? = nil
let width = CVPixelBufferGetWidth(sourcePixelBuffer)
let height = CVPixelBufferGetHeight(sourcePixelBuffer)
let pixelFormat = CVPixelBufferGetPixelFormatType(sourcePixelBuffer)
let attributes = CVBufferGetAttachments(sourcePixelBuffer, .shouldPropagate)!
CVPixelBufferCreate(nil, width, height, pixelFormat, attributes, &pixelBuffer)
CVBufferPropagateAttachments(sourcePixelBuffer, pixelBuffer!)

var filteredPixelBuffer = pixelBuffer!      // this never works
filteredPixelBuffer = sourcePixelBuffer     // 0_0

let context = CIContext(options: [kCIContextOutputColorSpace: CGColorSpace(name: CGColorSpace.sRGB)!])
context.render(filteredImage, to: filteredPixelBuffer)  // modifying original image buffer here!

let presentationTimestamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
var timing = CMSampleTimingInfo(duration: kCMTimeInvalid, presentationTimeStamp: presentationTimestamp, decodeTimeStamp: kCMTimeInvalid)

var processedSampleBuffer: CMSampleBuffer? = nil
var formatDescription: CMFormatDescription? = nil
CMVideoFormatDescriptionCreateForImageBuffer(nil, filteredPixelBuffer, &formatDescription)
CMSampleBufferCreateReadyWithImageBuffer(nil, filteredPixelBuffer, formatDescription!, &timing, &processedSampleBuffer)

print(assetInput!.append(processedSampleBuffer!))

当然，我们都知道不允许修改示例缓冲区，但以某种方式进行此方法可以得到正常处理的视频。这个技巧很“dirty”，我不能确定在具有预览层或某些并发处理程序的情况下是否可行。

- Varrry