To me it just sounds like something else is possible running and taking up processor power - causing the movie not to play smothly.
I would disable virus scan during playback - make sure other programs are not running. (Possible do a fresh reboot of the laptop before playing the movie.)
(gem) Hvis du ikke ønsker at andre kan se hvad du laver, kan du skifte over til "cloak mode" i indstillingerne. (Kun for betalende medlemmer) (pauloaguia) (vis alle tips)