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

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))
        } 
    }