My standalone DVD player supports playback of all regions and plays PAL DVDs & PAL VCDs perfectly. But when I play NTSC DVDs & NTSC VCDs the video jitters when there are fast movements.

When I play the NTSC DVDs & NTSC VCDs on my computer's DVD ROM Drive I also notice some jitters but I notice more when the NTSC DVDs or VCDs are played by my home DVD Player.

Does anyone know why these anoying jitters occur in NTSC DVDs and NTSC VCDs and what I can do to remove these jitters.