record clips from the played video and save them on the server

I want the client application to make / record clips from the played video and save them on the server. I have some idea of netstreams and know netstream.publish is used to save recorded video on the server. All the examples i find are of recording from webcam, i haven't found a way to set the streamed video as the source / input for the netstream to publish.

Help in this regard is greatly appreciated. Thanks.