As a Canon Vixia HF R21 user, we always met troubles in transferring Canon HF R21 AVCHD to iMovie editing as the different codecs between Canon R21 and iMovie. The codec of recordings from Canon Vixia HF R21 is MPEG-4-AVC/H.264, the AVCHD is highly compressed and not the iMovie friendly video format, but Apple Intermediate Codec(AIC) is the most compatible codec for iMovie. So if we want to edit AVCHD clips from Canon R21 in iMovie, a powerful third party conversion software is necessary.
If we have the best Canon Vixia HF R21 MTS conveter, it is easy for us to transcode MTS videos to AIC for iMovie. I used Brorsoft AVCHD to AIC for iMovie Converter, it is really a very easy-to-use tool for me.
Step 2: Click "format" bar to choose the compatible output format for iMovie.
Click and choose "iMovie and Final Cut Express--> Apple Intermediate Codec(AIC)(*.mov)"
Step 3: You can click "settings" to customize the output parameters, adjust the resolution, bitrate as you want. Set video size as 1920*1080, video frame rate as 30fps is better (If the original recordings are 1080 50i, pls set 25fps)