That's my site. I don't mention it here because Lordsmurf hates AmarecTV with a passion.
I think the issue is only the way it is being displayed by MPV. DV files have the proper display aspect ratio embedded, so they properly display at 4:3.
On the other hand, analogue AVIs such as most captures normally don't have the display aspect ratio embedded, so the player doesn't know how to display them.
I think the DV image is correct, the LAGS image is stretched.
I'm not familiar with MPV, but you can check what a file really looks like in VDub: open it and then on the video itself, right-click and choose 4:3. This will display the video in 4:3, and you should find it will look very similar to the DV version.
Ayarei beat me to it.