[Andersen smith]

iMovie will allow you to import the following file formats: MPEG-2 and
AVCHD from Camcorders, DV (standard definition) and HDV (high
definition), MPEG-4, DV, and .MPG files stored in Mac. If you want to
import iPod and iPhone video files .mp4 into imovie, you should
convert iPod and iPhone video files .mp4 to iMovie support video
formats.

MP4 to iMovie Converter not only can import mp4 into imovie on Mac OS
X, but also can import WMV, MP4, MOV, M4V, AVI, FLV, 3GP, 3GPP, 3G2,
MPG, VOB, MPEG, MPG, ASF, MOD, MKV, HD video (Convert ts, tp, trp,
m2ts, mts for Mac), etc . into iMovie on Mac OS X. MP4 to iMovie
Converter is the most powerful Mac Video Converter for you to import
video on Mac OS X (Leopard supported).

How to import .mp4 video files into imovie on mac os x?

http://www.4yousoft.com/imovie/mp4-to-imovie.htm

Step 1: Download, install and run MP4 to iMovie Converter
It's simple and quickly.

Step 2: Add .mp4 video files
Click the "Add files" button to import your mp4 files. This mp4 into
imovie converter support batch conversion, so you can import multiple
files at a time.

Step 3: Select output format: "MPEG-4 Movie (*mp4)"

Step 4: Convert
Click "Convert" button, it begins to convert your .mp4 files to imovie
mp4 format.

Step 5: Importing convertion mp4 files to imovie
Launch iMovie, go to "file import movies". Select the converted MP4
video then click "import".

http://www.4yousoft.com/imovie/mp4-to-imovie.htm