iOS - Screen capture a video

UIGetScreenImage() is a private API of Apple and they won't let me use it. I was using it to take a snapshot image of a full screen video and then saving the snapshot to the photo album. They suggest I in turn use AVCaptureSession to get my "screenshot" for my video. But the issue is I am streaming live vide开发者_StackOverflow中文版o and am unsure if the capture session will allow me to take a snapshot of the playing video. Any suggestions? If this doesn't work is there an Open-GL solution that would work?