Why We often Encounter Problem in Importing AVI to FCP X?
AVI (Audio Video Interleaved) is common video file format, which has better compatibility with Windows OS X. It can be easily playable on Windows Media Player or Movie Maker. However, to Mac user, AVI file format is their nightmare. It is because of their variant codecs. (Get free AVI player for Mac) 
FCP is a popular Mac editing software. It provides non-linear, non-destructive editing of any QuickTime compatible video format, including H.264 or MPEG compression, can support limited file formats like MP4, DV, MOV, M4V, and some AVI files from Cameras. However it only imports DV-AVI. If you try to add other AVI files like DivX-AVI, MJPEG-AVI, Xvid-AVI, 3ivX-AVI and more to FCP X, it either ends in fail or encounters some audio or video problem. Unsupported AVI video often comes from Sony camera, Canon camera, Nikon camera, Carton videos, and downloaded websites. So if your source AVI files can’t be accepted by Final Cut Pro X, you need to convert AVI to FCP compatible code Apple ProRes. I know a program that named iMedia Converter for Mac, is just the ideal AVI to Prores conversion software. It can easily transcode any kind of AVI video to Prores .mov for adding AVI to Final Cut Pro X for editing. Below is a step by step guide to show you how to convert avi videos to FCP X. Preparation: Run Pavtube AVI to FCP Converter Download and install the Mac AVI to ProRes converter on your Mac computer, it works on Mac OS 10.5 or above. 
Step 1. Run the program and load your AVI video files into it. 
Step 2. Choose Apple ProRes 422 (*.mov) as output. You can easily find it in “Final Cut Pro” category. (Learn Types of Apple ProRes Codecs) 
Step 3. Start transcoding AVI to Apple ProRes by clicking on “Convert” button. Of course, the process will take some time, please wait patiently. When it’s finished, you can easily import the converted media file into FCP X for editing. Except help you handling AVI video files, this all-in-one Mac Ultimate Converter can deal with Blu-ray, DVD and almost all the camera footage from Canon, Sony, Panasonic, JVC, Nikon etc. Meanwhile, it’s able to convert a wide range of video formats for your tablets or smartphones with optimized presets. Overall, it’s really a good helper that worth having.