iMovie is a proprietary video editing software application sold by Apple Inc. for the Mac and iOS (iPhone, iPad, iPad Mini and iPod Touch). It was originally released in 1999 as a Mac OS 8 application bundled with the first FireWire-enabled consumer Mac model – the iMac DV. Since version 3, iMovie has been an OS X-only application included with the iLife suite of Macintosh applications.
iMovie imports video footage to the Mac using either the FireWire interface on most MiniDV format digital video cameras, the USB port, or by importing the files from a hard drive. From there, despite its simplicity, iMovie offers many of the same features - the user can edit the video clips, add titles, and add music. Effects include basic color correction and video enhancement tools, and transitions such as fade-in, fade-out, and slides.
Starting with version 5 (from 2005), iMovie processes high-definition video from HDV camcorders, in later versions also from AVCHD camcorders and H.264-compressed video from MPEG-4 or QuickTime Movie files (.mov)., e.g. as generated by a number of digital photo cameras with HD video recording feature. To facilitate this, iMovie/iLife installs the Apple Intermediate Codec on the system as a QuickTime component. iMovie transcodes ('optimizes') HD video upon ingestion ('import') using this codec and stores it in the QuickTime file format (.mov).
Since iMovie doesn't natively support all video formats, if you have some unaccepted files like .mts/.m2ts/.avi/.mpg, etc and want to edit them in iMovie, you have to convert them to iMovie-friendly formats such as Apple AIC via iOrgsoft AVCHD Converter for Mac before importing.