How can I remove or reduce moire in FCPX?

Moiré is an artifact visible from interference between two frequencies. In your case, the video has some horizontal pattern that is conflicting with the scan lines on your display. The artifact may not actually be there on a finished movie since FCPX's viewer scales. But, you change the freq of one of the sources and the moiré usually goes away or is diminished. You can scale the video a few percent or you can apply one or two pixels of blur or both.

Before you do that, try to be sure it's not just a weird manifestation of your editing monitor.

Forgot to mention if you scale up,say, two percent, you can move the image up or down a pixel or fraction of a pixel or even rotate it slightly, That reduces the interference.

Is the shot static or in motion?

MtD

That moiré was recorded that way, interference was caused by the blinds interacting with either your sensor or horizontal lines on the glass. That, I'm afraid, you live with. However, have you tried searching for moiré reduction filters? There might be something from FxFactory for After Effects or Motion. Might be worth $50?

Please come back and let us know if you find something useful.

In the screen shot you posted, the moire is appearing as variations of color (caused in the case of the windows by the horizontal lines in the blinds) - is that correct?

Not sure what the procedure would be in FCP-X but, at least to correct the moire in the windows, I would export a frame from the editor, and take that exported frame into Photoshop, and in Photoshop cut a matte in for the areas where the moire is visible. Import that matte into the editor, and then use the matte to composite an identical image where the saturation had been pulled back to near monochrome so the color ringing is less apparent.

MtD