How to choose a Frame grabber?

Hello everybody,
I need some help choosing a frame grabber.
I'm interesetd in simple applications and I need a frame grabber that
provides not only compressed stream or compressed images but also
bitmap frames. It is for teaching applications.
Can you provide me some indication/name of frame grabber that supports
this characteristics?
If you don't want to give name of commercial products on the NG, can
you send me a mail?
Thanks a lot Giovanni

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