To which format should I convert to enable swift 'scanning' of a file?

I mean by that pulling the slider and seeing the movie slide by, every frame, as I pull it. Stop pulling and it stops at that place.
Press continue and it carries on at normal speed. Or pull the slider again and off we go again.

I know this can happen because I've seen it somewhere. Done it.

But it doesn't happen with my .asf files in VLC or Media Player Classic.

And when I convert them to mp4 it still doesn't happen.

These .asf fles are produced by surveillance camera software. It will not make any other kind. It does provide its own scanning utility but it performs the same way VLC and MPC do.

That is the pic freezes while you pull the scanner (or sometimes seems to continue playing from the previous place) and when you stop the film stops there, too. If I release the mouse button then the slider will fly back to where it was in VLC and MPC. In the proprietary software it will at least stay where we now are, but we still didn't get to see all that happened between the starting place and this end place.

I just had a thought. I think it was something called Magix or something similar that I used to see this function working on. I don't have it on this computer. I'll go see if I can find it and see if it will accept these .asf or the .mp4 and see if it will do what I want.

Maybe I've solved the problem myself.....

But maybe not. I would still like any input I can get on the question.

I have dozens of hours of surveillance video to scan and I simply can't do it other than by sitting and watching them play in real time - you can imagine what chance I've got of being able to do that.