download it from the Squared5 website. Just drag your movie onto the MPEG Streamclip interface, go to the File menu and choose Export to MPEG-4. Then choose H.264 as the video compression and set the quality to 100%. It does a nice job of converting the video while maintaining quality.
UPDATE: If you're using Premiere to export your videos, I've found that using H.264 as the video Format will save the movie with AVC Coding. However, if you select QuickTime as the Format and set the Video Codec to H.264, you can get a movie that works with MovieCaptioner right out of the gate.