Well, you may take tons of videos and pictures on your iPhone or camcorder/camera every day, and after you copy these files to Mac iPhoto, you may confuse by iPhoto because many people failed to export their own videos from iPhoto.
As we all know, iPhoto by default will manage your iPhoto Library for you, everytime you import a new photo or video, it will automatic copy your files to the library and leave the original ones untouched on your Mac. Of course, you can change the settings and let iPhoto points to your original files on Mac rather than copying them to library: Go to iPhoto Preferences > Advanced, and unchecked the box of "Copy items to the iPhoto Library", then you won't have any problem to deal with your photo and videos on Mac.
Tips: In this case, you have to ensure that your original videos are in the original locations/folders, otherwise they will not work in iPhoto. If you move your original files after importing to iPhoto, you need to delete your current iPhoto library by dragging to the trash, and then re-import everything from your new location/folder.
For those videos files already stored in the iPhoto library, you will need to export videos from iPhoto if you want to access to the original files or export the edited iPhoto movies. No solution for this problem? Just read on and follow this tutorial to get your movies out of iPhoto library:
Step 1. Select the videos you intend to export in iPhoto, and click File > Export.
Step 2. In the export dialog, the defaulted Kind of the file is set to JPEG, so you need to change it to Original so that you can export your video or movie from iPhoto.
Step 3. Click the "Export" button and choose the output folder to save your video. Done! Now you could edit your exported videos in iMovie, or upload them to YouTube for sharing, or do anything to your movies after getting them out of iPhoto. Just enjoy them!
Tips: There's an easier way to export or transfer videos from iPhoto to iMovie: Just open iMovie and on the left of the Event Library you'll see a section called iPhoto Videos. If you can't see the iPhoto Videos section click on the little arrow next to the name of your hard drive just under the Last Import section in the Event Library. If you need to export iPhoto video to iMovie, you need to convert iPhoto video to iMovie compatible MP4, MOV video files