It should work. It is on the supported list.
I suggest that you right click on the Event clips (or possibly the Event Name) and see if it offers to optimize your clips. If so, optimization will improve the performance.
When you optimize, it converts to Apple Intermediate Codec. It gets larger in the process. For a sense of why this is so, see this post. H.264 and AVCHD are both highly compressed formats that are good for capture and delivery, but not for editing. iMovie converts AVCHD to Apple Intermediate Codec automatically, but with h.264 you have a choice. This is probably because not all h.264 files are HD.
If you have optimized and it is still sluggish, there may be something else going on. I doubt it is your Mac if the Nikon footage works, but you didn't say what kind of Mac you have.
Thanks for the repy. It helped me a lot.
Apple Support suggests me to import in 960 x 540 size, but it really seems to reduce significantly the resolution achievable by the Canon DSLR. I want to edit with original video quality, which is so hard.
The recorded file is 1080@30fps.
Mac OS X Mountain Lion 10.8.
I would suggest staying on 1920x1080 and converting to Apple Intermediate Codec.
If you did not get the option to optimize, you can do it using an external free tool called MPEG Streamclip.
Drag your original clip into MPEG Streamclip. Then use FILE/EXPORT TO QUICKTIME and choose Apple Intermediate Codec for the Video Compression.
Thank you for reminding me of the conversion. Yes, I can convert my video to AIC for editing with iMovie 11.
I have tried to use the free MPEG Streamclip tool, but it makes me unhappy. It is liable to crashes and I have to install the quicktime. I don't like it. I will go to Google to look for a professional convert tool.
Anyway, thanks a lot for your help. Happy New year.
Hi, Matty Apple, I'm very glad to hep you solve the problem.
iMovie 11 supports to edit the recorded H.264 video files from 5D Mark iii, but it need a powerful Mac system with a large memory. If not, you won't smoothly edit the files. Besides, as far as I know, you can't edit the files with original quality.
You can use the professional Mac Video Converter from Brorsoft to transcode Canon 5D Mark video to Apple Intermediate Codec. It is easy to use, you can have a try.