[Zane Barker] “Different audio codecs easily explains the file size difference, as well as that is why FCP always wants to render files captured in iMovie when they are brought into FCP.
“
No, it’s not the codec that’s different. iMovie captures as DV Stream, which locks the audio and video.
FCP does not recognize “muxed” media from iMovie, and hence has to split the audio off, ie render.
But the camera is recording the DV Codec.
Cheers
Alexander