From the document.apple, you can know that Final Cut Pro is well compatible with QuickTime files like MOV, DV, etc. However, to AVI files, it depends. AVI filess are often containers, which may come from different codecs like DivX, Xvid or 3ivX. Not all the codecs can be imported into the FCP. So if you intend to use the FCP to edit AVI file, you need to convert FCP to QT compatible file formats like MOV or MP4, then import AVI to Final Cut Pro.

The Mac Video Converter can not only convert AVI to FCP for editing, but also make you edit some unsupported AVI into iMovie. Plus, it can act as practical editing jobs like video trimming, video cropping or add some artistic effects and so forth.

Easy guide on how to import AVI into FCP for editing on Lion OSX:

Firstly, download the Mac AVI to FCP Converter on Mac Lion OSX. Install and run it.

Secondly, load the .avi file into the application. If you try to edit multiple .avi files, please add several files at one time. For the software can support batch conversion. Then, choose the right file format for Final Cut. Select the QuickTime MOV as output file format, you can get the optimal video quality.

Thirdly, hit "START" to do the conversion. Supposed you don't want to edit clips with software.

The last step, directly import the generated .mov file into FCP project and go on the editing movie in Final Cut Pro.