Uploading to YouTube?

Hi guys-- when I upload a video to YouTube straight from iMovie, it says "creating movie" before it uploads. The thing is, the "creating movie" step takes up a lot of drive space that doesn't restore itself after the movie is uploaded to YouTube. Does anyone know where iMovie stores these "created" movies on my computer? (This doesn't apply to regular movies that I export to my computer, just the ones that I put on YouTube.)

Any help would be appreciated! 🙂