Before you can add your own videos, you must first make them available on your iOS device by syncing with iTunes. To learn about syncing, click the Help menu in iTunes and search for "Convert a video for viewing on iPod, iPhone, or iPad."

Once you've synced videos to your iOS device, follow these steps to add a video to a Keynote slide:

1. Tap the Media window icon at the top-right of the display in Keynote for iOS:
2. When the Photo Albums page opens, tap Media.
3. Tap the photo album that contains your video.
4. Tap the video thumbnail you want.
5. Tap Use. The video and its audio track will play automatically when the slide is played by tapping the play icon: