I didn’t know about this:
Once you have gotten the digital video of the film you will be commenting on, you will need to both get the specific clips you want to talk about and compress them. We recommend you use a tool like MPEG Streamclip (PC/Mac). Important: When using a Mac or PC and working with video editing/conversion tools like MPEG Streamclip (or any of the others listed above) it is highly recommend that you make sure to install Perian (for the Mac) or the K-Lite Codec Pack(for the PC)—both of which are free utilities that add a series of codec recognition tools across the various video applications on your computer.
What MPEG Streamclip will allow you to do is select and trim exactly the clips you want to discuss from the longer scenes. Doing this in MPEG Streamclip will save you time and energy before importing it into a video editor like Moviemaker or iMovie, both of which bloat video unnecessarily and take a lot more time and resources to work with. Note that you may have to cut a longer scene up into various clips that you will then edit together in your final version. Also, when converting the clips, make sure they are the same aspect ratio as the original, and that you are saving them in the proper codec for your video editing software. (Note: MPEG Streamclip will convert files to Windows media format.)