Screencaps from FLV, native PHP function, raw keyframes data

I'm not sure if this is even possible to implement in any simple way, so do not bid unless you know for sure that you can handle this project. Your goal will be to develop small function in PHP, which will be able to get random keyframes from FLV video file in order to create screenshots from the video. Given keyframe image will be then processed using imagecreatefromstring() and saved to disk as JPG (server has support for image functions). It is not possible to install any PHP extensions to the server, it is not possible to use any huge classes, it is not possible to call any external binary. You'll have to implement raw access to the FLV file to get some keyframes, preferably one image for every 60 seconds of the video.