MOV file causes 100% CPU

[CatKiller]

Have a look for updated drivers for your graphics

It's not the graphics driver, it's the lack of VDPAU. There is a package to translate Intel's VA-API into the VDPAU that the application is expecting. Or the OP could use the -vo vaapi -va vaapi mplayer options directly. But the OP would prefer not to use hardware acceleration for some reason, apparently.

[Yellow Pasque]

It's not the graphics driver, it's the lack of VDPAU. There is a package to translate Intel's VA-API into the VDPAU that the application is expecting.

IIRC, the package you are referring to is libvdpau-va-gl1. But if you have an Intel GPU, you should not be using VDPAU unless it's your only option. Using VA-API directly will give better performance.

sudo apt-get install i965-va-driver vainfo

Then, you need a player capable of using VA-API. I'd recommend mpv (with smplayer as a front-end GUI if you wish). I don't think the old mplayer supports VA-API unless you get the specially patched version of it.

[mc4man]

Install & run vainfo, see if hevc (h.265) is supported. If so you can use vaapi hwdec though not in mplayer. In that case try mpv instead.

Edit: The video likely is supposed to be played back at either 30 or 60 fps, that's what creates the slo-mo. Maybe your players are trying to play at 240fps?
(- you could try something like

mplayer --no-correct-pts --fps=30 or mplayer --no-correct-pts --fps=60

mpv has similar options..