detect analog video signal and record only when present

[ecloud]

I'm still trying to digitize old laserdiscs and videotapes. I can now capture with audio, crop, deinterlace and save to various file formats. But so far I'm specifying how many seconds to capture, which is always a guess, so there is a blue screen for some time at the beginning (because I have to press Play by hand) and at the end (when I guess wrong about the length). It would be nice if VLC could wait for a live video signal to be present, and then auto-stop when the video signal goes away again. Is that possible?