Fastest way to record video from SCNView - ios

Question

I have SCNView with some object in the middle of screen, user can rotate it, scale, etc.
I want to record all this movements in video and add some sound in realtime. Also I want to record only middle part of SCNView (e.g. SCNView frame is 375x812 but I want only middle 375x375 without top and bottom border). Also I want to show it on screen simultaneously with video capturing.
My current variants are:
func renderer(_ renderer: SCNSceneRenderer, didRenderScene scene: SCNScene, atTime time: TimeInterval) {
DispatchQueue.main.async {
if let metalLayer = self.sceneView.layer as? CAMetalLayer, let texture = metalLayer.currentSceneDrawable?.texture, let pixelBufferPool = self.pixelBufferPool {
//1
var maybePixelBuffer: CVPixelBuffer? = nil
let status = CVPixelBufferPoolCreatePixelBuffer(nil, pixelBufferPool, &maybePixelBuffer)
guard let pixelBuffer = maybePixelBuffer else { return }
CVPixelBufferLockBaseAddress(pixelBuffer, [])
let bytesPerRow = CVPixelBufferGetBytesPerRow(pixelBuffer)
let region = MTLRegionMake2D(Int(self.fieldOfView.origin.x * UIScreen.main.scale),
Int(self.fieldOfView.origin.y * UIScreen.main.scale),
Int(self.fieldOfView.width * UIScreen.main.scale),
Int(self.fieldOfView.height * UIScreen.main.scale))
let pixelBufferBytes = CVPixelBufferGetBaseAddress(pixelBuffer)!
texture.getBytes(pixelBufferBytes, bytesPerRow: bytesPerRow, from: region, mipmapLevel: 0)
let uiImage = self.image(from: pixelBuffer)
CVPixelBufferUnlockBaseAddress(pixelBuffer, [])
//2
if #available(iOS 11.0, *) {
var pixelBuffer: Unmanaged<CVPixelBuffer>? = nil
CVPixelBufferCreateWithIOSurface(kCFAllocatorDefault, texture.iosurface!, nil, UnsafeMutablePointer<Unmanaged<CVPixelBuffer>?>(&pixelBuffer))
let imageBuffer = pixelBuffer!.takeUnretainedValue()
} else {
// Fallback on earlier versions
}
//3
var pb: CVPixelBuffer? = nil
let result = CVPixelBufferCreate(kCFAllocatorDefault, texture.width, texture.height, kCVPixelFormatType_32BGRA, nil, &pb)
print(result)
let ciImage = CIImage(mtlTexture: texture, options: nil)
let context = CIContext()
context.render(ciImage!, to: pb!)
}
}
}
Obtained CVPixelBuffer will be added to AVAssetWriter.
but all of this methods have some flaws.
1) MTLTexture has colorPixelFormat == 555 (bgra10_XR_sRGB if I recall correctly) and I don't know how to convert it to BGR (to append it to the aseetWriter) nor how to change that colorPixelFormat nor how to add bgra10_XR_sRGB to the aseetWriter.
2) How to implement version for iOS10?
2,3) What is the fastest way to crop an image? Using this methods I can grab only full image instead of cropped one. And I don't want to convert it to UIImage because it too slow.
P.S. my previous viewer was on OpenGL ES(GLKView) and I successfully did it using this technique (overhead 1ms instead of 30ms using .screenshot method)