Apple Keynote (Macintosh Only)
Step 1: See the section on Record a voiceover narration at Keynote for Mac: Add video and audio
Step 2: Keynote for Mac: Save a presentation in another format
NOTE: If you created your narrated presentation on a Mac using PowerPoint, the audio will not play in the video. You can how ever take the .ppt file to a Windows computer, open it in PowerPoint and covert it to a video.