.iso is a disk image, DVD is an optical disc format, and MPV is a software media player. None of these really have anything to do with anything.
You're probably dealing with MPEG-2 video (what was standard on DVD) with low frame rates and the player is trying (badly) to fill in the gaps. But let me be clear, I'm not besmirching MPV, it's probably doing the best it can. It's probably the source. If it's from DVD, it's max 720x480 (16:9; 640x480 for 4:3, not sure what these old Naruto eps are in). So you could do better with some webrip from Crunchy or whatever where it's 1080p, either natively or, for the old Naruto, possibly upscaled. Or just find it in 720p (1280x720).
(Just checked mine, it's 480p.) (Let me know what episode and time stamp this is and I'll check mine.)

