Some video stutters in panning scenes

Is this a codec issue or a hardware issue?

Only happens in some videos.

This is on an older PC: i5 760 + AMD 5770

Still wouldn't expect this hardware to stutter in a panning scene. So maybe it is a codec?

It's possibly a driver issue. If I recall some older Radeons had some issues with hardware accelerated decoding problems so you might want to disable video acceleration and see if it goes away. Otherwise try playing the video back in VLC media player (because it doesn't use Windows Directshow Codecs).

As always, update to the newest drivers first.

Will an i5 760 be able to cope on its own, without the support from the video card?

I always see people talking about disabling hardware acceleration as if the video card is irrelevant.

Which Windows theme are you using?

To clarify, if you're on Windows 7 using any of the non-accelerated themes you'll get tearing (including videos).
Not sure about Windows 8.