如何提高将 UIImage 转换为 CVPixelBuffer 的性能？

Question

我有一个UIImage 数组，里面有很多UIImage 对象，并使用link 中提到的方法将图像数组导出为视频。一切正常，但是将UIImage 数组转换为CVPixelBuffer 的性能非常糟糕：

    private func newPixelBufferFrom(cgImage:CGImage) -> CVPixelBuffer?{
    let options:[String: Any] = [kCVPixelBufferCGImageCompatibilityKey as String: true, kCVPixelBufferCGBitmapContextCompatibilityKey as String: true]
    var pxbuffer:CVPixelBuffer?
    let frameWidth = self.videoSettings[AVVideoWidthKey] as! Int
    let frameHeight = self.videoSettings[AVVideoHeightKey] as! Int

    let status = CVPixelBufferCreate(kCFAllocatorDefault, frameWidth, frameHeight, kCVPixelFormatType_32ARGB, options as CFDictionary?, &pxbuffer)
    assert(status == kCVReturnSuccess && pxbuffer != nil, "newPixelBuffer failed")


    CVPixelBufferLockBaseAddress(pxbuffer!, CVPixelBufferLockFlags(rawValue: 0))
    let pxdata = CVPixelBufferGetBaseAddress(pxbuffer!)
    let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
    let context = CGContext(data: pxdata, width: frameWidth, height: frameHeight, bitsPerComponent: 8, bytesPerRow: CVPixelBufferGetBytesPerRow(pxbuffer!), space: rgbColorSpace, bitmapInfo: CGImageAlphaInfo.noneSkipFirst.rawValue)
    assert(context != nil, "context is nil")

    context!.concatenate(CGAffineTransform.identity)
    context!.draw(cgImage, in: CGRect(x: 0, y: 0, width: frameWidth, height: frameHeight))
    CVPixelBufferUnlockBaseAddress(pxbuffer!, CVPixelBufferLockFlags(rawValue: 0))
    return pxbuffer
}

你能给我一些想法吗？
谢谢！

Answer 1

我解决了我的问题。
在我的视频编辑应用程序（如 iMovie）中，我需要将一张图像转换为视频并使图像（现在是视频）可移动。
UIImage 数组本质上来自 UIImage。因此，我避免多次但只调用一次newPixelBufferFrom。以下代码会更快：

    var sampleBuffer:CVPixelBuffer?
    var pxDataBuffer:CVPixelBuffer?

    let options:[String: Any] = [kCVPixelBufferCGImageCompatibilityKey as String: true, kCVPixelBufferCGBitmapContextCompatibilityKey as String: true]
    let frameHeight = self.videoSettings[AVVideoHeightKey] as! Int
    let frameWidth = self.videoSettings[AVVideoWidthKey] as! Int
    let originHeight = frameWidth * img!.cgImage!.height / img!.cgImage!.width
    let heightDifference = originHeight - frameHeight

    let frameCounts = self.duration * Int(self.frameTime.timescale)
    let spacingOfHeight = heightDifference / frameCounts

    sampleBuffer = self.newPixelBufferFrom(cgImage: img!.cgImage!)
    assert(sampleBuffer != nil)

    var presentTime = CMTimeMake(1, self.frameTime.timescale)
    var stepRows = 0

    for i in 0..<frameCounts {
        CVPixelBufferLockBaseAddress(sampleBuffer!, CVPixelBufferLockFlags(rawValue: 0))
        let pointer = CVPixelBufferGetBaseAddress(sampleBuffer!)
        var pxData = pointer?.assumingMemoryBound(to: UInt8.self)
        let bytes = CVPixelBufferGetBytesPerRow(sampleBuffer!) * stepRows
        pxData = pxData?.advanced(by: bytes)

        let status = CVPixelBufferCreateWithBytes(kCFAllocatorDefault, frameWidth, frameHeight, kCVPixelFormatType_32ARGB, pxData!, CVPixelBufferGetBytesPerRow(sampleBuffer!), nil, nil, options as CFDictionary?, &pxDataBuffer)
        assert(status == kCVReturnSuccess && pxDataBuffer != nil, "newPixelBuffer failed")
        CVPixelBufferUnlockBaseAddress(sampleBuffer!, CVPixelBufferLockFlags(rawValue: 0))

        while !self.writeInput.isReadyForMoreMediaData {
            usleep(100)
        }
        if (self.writeInput.isReadyForMoreMediaData){
            if i == 0{
                self.bufferAdapter.append(pxDataBuffer!, withPresentationTime: zeroTime)
            }else{
                self.bufferAdapter.append(pxDataBuffer!, withPresentationTime: presentTime)
            }
            presentTime = CMTimeAdd(presentTime, self.frameTime)
        }

        stepRows += spacingOfHeight
    }