Sometimes when using a velocity envelope a clip appears to quickly go in and out of focus repeatably. Any idea what causes this or a fix?

Is it only during preview? Or after a render? If it's during the preview, turn off the "Adjust size and quality for optimal playback" option.

Thank you Edward. It is after the render. But I can remove the envelope and render and it is fine. Doesn't do it all the time. Seems to be worse on pans.

It could be interlacing issues, then. Try changing the interlacing settings to different values until you find the setting you like best.

You did check "disable resample" on your video event?

Thanks guys. I'm out of town right now but will check on those things as so as I return home.