Video stutter in viewer

Hi first post sorry if there is an answer to this problem elsewhere, I have looked but can't seem to find one.

The problem is that when watching back certain footage in the viewer (only certain material) it stutters and seems to be playing in slow motion. The audio is fine and once a put in on the time line it plays smoothly.
Have tried refeshing av devices and fit to window in viewer options.

Have you any idea how I can fix this?

Thanks for any help

Tomo

Do you have Unlimited RT on? If so is there an Orange line above your footage in the timeline? Unlimited RT will attempt to play your footage even if your computer or sequence is unsuited to doing so. To manage it, FCP will degrade the quality and drop frames.

As a general rule of thumb, I don't edit in Unlimited RT unless I need to look at something specific that would otherwise take several long renders.

On the upper left side of your timeline is a button that says RT. Click on it and then choose SAFE from the menu. Render your footage.

Andy