The command is somewhat hidden, but if you go to the File menu, choose Save & Send, then Create a Video (a screenshot is at left). You be given options to choose a screen resolution, choose existing slide timings and narration, set new timings and narration, or give each slide a predetermined amount of time (e.g. 5 seconds). Click the Create Video button and you're done. Be aware that long or complex PowerPoints will take some time to render.
If you have a video embedded within your PowerPoint it will automatically play when the presentation gets to that slide.
Below is a very short PowerPoint on Password Protection rendered into a video, with 5 seconds per slide.
