Rotate CMSampleBuffer by arbitrary angle and append to AVAssetWriterInput in swift 3 - ios

Question

I convert the sample buffer to a CGContext. Then I apply a transformation to the context and create a CIImage from that, which in turn gets displayed in an UIImageView.
At the same time I want to append this to the AVAssetWriterInput to create a movie of these transformations.
So far the transformations I apply to the context have no effect whatsoever. When I display the so called transformed image in the imageview. it looks exactly the same.
UPDATE:
I managed to record the sample buffer to a video file (it's still stretched because of the wrong orientation though). I've used this code as a base
http://geek-is-stupid.github.io/blog/2017/04/13/how-to-record-detect-face-overlay-video-at-real-time-using-swift/
But I'm still struggling with applying the rotating to the CGContext. basically everything I do to the context is completely ignored.
func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!) {
let writable = canWrite()
if writable , sessionAtSourceTime == nil {
print("starting session")
sessionAtSourceTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
assetWriter!.startSession(atSourceTime: sessionAtSourceTime!)
}
let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
if writable {
autoreleasepool {
CVPixelBufferLockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
var renderedOutputPixelBuffer: CVPixelBuffer? = nil
let options = [
kCVPixelBufferCGImageCompatibilityKey as String: true,
kCVPixelBufferCGBitmapContextCompatibilityKey as String: true,] as CFDictionary
let status = CVPixelBufferCreate(kCFAllocatorDefault,
CVPixelBufferGetWidth(pixelBuffer),
CVPixelBufferGetHeight(pixelBuffer),
kCVPixelFormatType_32BGRA, options,
&renderedOutputPixelBuffer)
guard status == kCVReturnSuccess else { return }
CVPixelBufferLockBaseAddress(renderedOutputPixelBuffer!,CVPixelBufferLockFlags(rawValue: 0))
let renderedOutputPixelBufferBaseAddress = CVPixelBufferGetBaseAddress(renderedOutputPixelBuffer!)
memcpy(renderedOutputPixelBufferBaseAddress,CVPixelBufferGetBaseAddress(pixelBuffer),CVPixelBufferGetHeight(pixelBuffer) * CVPixelBufferGetBytesPerRow(pixelBuffer))
CVPixelBufferLockBaseAddress(renderedOutputPixelBuffer!, CVPixelBufferLockFlags(rawValue: 0))
let context = CGContext(data: renderedOutputPixelBufferBaseAddress,
width: CVPixelBufferGetWidth(renderedOutputPixelBuffer!),
height: CVPixelBufferGetHeight(renderedOutputPixelBuffer!),
bitsPerComponent: 8,
bytesPerRow: CVPixelBufferGetBytesPerRow(renderedOutputPixelBuffer!),
space: CGColorSpaceCreateDeviceRGB(),
bitmapInfo: bitmapInfo!)
let radians : Float = atan2f(Float(boxView!.transform.b), Float(boxView!.transform.a));
context!.translateBy(x: self.view.frame.size.width/2, y: self.view.frame.size.height/2)
context!.rotate(by:CGFloat(radians))
let image: CGImage = context!.makeImage()!
self.imageView!.image = UIImage(cgImage: image)
if (bufferAdaptor?.assetWriterInput.isReadyForMoreMediaData)!, canWrite() {
bufferAdaptor?.append(renderedOutputPixelBuffer!, withPresentationTime: CMSampleBufferGetPresentationTimeStamp(sampleBuffer))
}
CVPixelBufferUnlockBaseAddress(renderedOutputPixelBuffer!,CVPixelBufferLockFlags(rawValue: 0))
CVPixelBufferUnlockBaseAddress(pixelBuffer,CVPixelBufferLockFlags(rawValue: 0))
}
}

Answer 1

found the solution. Below the important part of the code.
//create pixelbuffer from the delegate method samplebuffer
let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
CVPixelBufferLockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
//create CI image from the buffer
let ci = CIImage.init(cvPixelBuffer: pixelBuffer, options: options)
//create filter to rotate
let filter = CIFilter.init(name: "CIAffineTransform")
//create transform, move rotation point to center
var transform = CGAffineTransform(translationX: self.view.frame.midX, y: self.view.frame.midY)
//rotate it
transform = transform.rotate(angle: CGFloat(radians))
// move the transform point back to the original
transform = transform.translatedBy(x: -self.view.frame.midX, y: -self.view.frame.midY)
filter!.setValue(transform, forKey: kCIInputTransformKey)
filter!.setValue(ci, forKey: kCIInputImageKey)
//take the output from the filter
let output = filter?.outputImage
//create empty pixelbuffer
var newPixelBuffer : CVPixelBuffer? = nil
CVPixelBufferCreate(kCFAllocatorDefault, Int(self.view.frame.width) ,
Int(self.view.frame.height),
kCVPixelFormatType_32BGRA,
nil,
&newPixelBuffer)
//render the context to the new pixelbuffer, context is a global
//CIContext variable. creating a new one each frame is too CPU intensive
context.render(output!, to: newPixelBuffer!)
//finally, write this to the pixelbufferadaptor
if (bufferAdaptor?.assetWriterInput.isReadyForMoreMediaData)!, canWrite() {
bufferAdaptor?.append(newPixelBuffer!,
withPresentationTime: CMSampleBufferGetPresentationTimeStamp(sampleBuffer))
}
CVPixelBufferUnlockBaseAddress(pixelBuffer,CVPixelBufferLockFlags(rawValue: 0))