9Slides is a fantastic site/app for adding video/audio to a presentations. The way this works is simple, a user uploads a presentation file (PPT, Keynote, PDF, etc) and then can either add audio to narrate their presentation, or even a video. This is great for doing a Pecha Kucha style presentation and ideal for "flipping a classroom".
For a brief demo view below...
I highly recommend checking out 9Slides by clicking here!!!
*9Slides is an advertiser of Technology Tidbits.