[johnny cathcart] "H.264 - 1920 / 1080 - Editing timebase 23.98 0- Pixel Aspect Square"
A simple search on this forum would yield a few thousand posts that would indicate that h.264 is not an editing codec that's useable in FCP.
You must transcode your material to a "realtime FCP codec" such as ProRes 422 before editing.
David Roth Weiss
ProMax Systems
Burbank
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http://www.ProMax.com
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David is a Creative COW contributing editor and a forum host of the Apple Final Cut Pro forum. 
