MP4 is a final delivery lossy video format which is not suitable for editing in non-destructive video editing software like Final Cut Pro. Though Final Cut Pro 7 and Final Cut Pro X update to import MP4 video, it only support MP4 encoded with H.264. If the MP4 is encoded with other video codec, Final Cut Pro X/7 will still fail to import MP4.
In order to solve can't import MP4 to Final Cut Pro issue and successfully import various MP4 files to FCP or FCP X, a recommended solution is to convert MP4 to Final Cut Pro more compatible video format like Apple ProRes or DV at http://www.idealshare.net/imovie-fcp/mp4-final-cut-pro.html
