VLC Media Player , a freeware program for Windows, Linux and Mac OS X, can do screen captures from any video it can play, including DVDs. When you click the Video/Snapshot menu option, it puts a JPG or PNG file in whatever folder you designated as your Snapshot folder.
It won't do frame-by-frame advance, though. And when you click pause, the video comes to a rolling stop, so you may find it's not as precise as you're looking for. But at least it's free to try.
I've started using VLC as my default player for pretty much all video. I like the Video/Always on Top option to keep my other windows from overtaking the video, and I drag it over to the most out-of-the-way corner of the screen.
It's supposed to be able to stream video, but I've never tried that.
-- Lauren