I'm not a "professer" in the video editing program like Sony Vegas, iMovie, but I had the experience on them. For Sony Vegas, the best format is MPEG-2, WMV (VC-1) (*.wmv) or MOV (AVC)(*.mov). For iMovie, the best format is AIC MOV. You can just try to install these compatible codec. Or, just like me, use the Brorsoft Video Converter for Mac to recode your vido files first for these non-linear editing software.It offers the particular output profiles for iMovie, Sony Vegas, even FCP, Avid, etc. Good luck.