The codec is supported but it is a very odd aspect ratio and it is a very odd framerate.
The aspect ratio should be OK although it will need to be letterboxed in iMovie.
The frame rate is 6.1 frames per second. iMovie projects are usually 30 frames per second, but can be 24 frames per second at the slowest, so I don't know how it would react to something that is 6 frames per second. You rarely see something this slow unless it is from a security camera.
Also the audio is 16000 Hz. iMovie expects audio to by recorded at 48,000 Hz. The audio may work, but it will likely get out of synch with the video.
I would suggest that you get a free app called MPEG Streamclip. Here is a link.
Drag your h.264 file into MPEG Streamclip.
In MPEG Streamclip, see if it will play by pressing the Play button (or by tapping the space bar).
If it does, use FILE/EXPORT TO QUICKTIME.
Choose Apple Intermediate Codec for compression. For Sound choose Uncompressed 48 kHz.
For Frame size choose OTHER and type in 1440x900.
For Frame Rate, try 24, and check the box that says Frame Blending. (You may want to uncheck frame blending and try that as well.)
Uncheck the box that says Interlaced Scaling. If the final result looks bad, come back and try Interlaced Scaling / Upper Field First.
Click Make Movie and save it in a place you can find it.
Then open iMovie and use FILE/IMPORT MOVIE to import the new movie you just made.
At least that is what I would try.
it has an exotic resolution, an exotic audio setting, and finally: 6.12fps??? more a sort of fast slide-show than a movie
give the free converter Mpeg Streamclip a try to convert this into a video format.
for usage in iM, convert to AppleIntermediateCodec, set correct framerate, resize to your Projects settings (1080 or 720)
keep in mind:
iMovie is by concept meant for camcorder imports - any 'files' off those handful of standards are usually a NoGo.
< aarghgh, beat by the minute and Mr Appleman ... again! have to learn typing faster! >