When you’re delivering your presentation, you may want a video to play automatically as soon as the slide it's on appears onscreen.
Play a video automatically when a slide appears in Slide Show
In Normal view, click the video in your slide.
Under Video Tools, click the Playback tab.
Next to Start, click the down arrow, and select Automatically.
When you are delivering your presentation in Slide Show View or Presenter View, the video will play automatically when you arrive at the slide.
If your slide doesn’t have a video in it yet, you can add one. Go to Add and play a video in a presentation for more information.
Important: Certain older video file formats may not compress or export properly in Office on a Windows RT PC. Instead, use modern media formats such as H.264 and Advanced Audio Coding (AAC), which PowerPoint 2013 RT supports. Want to know what version of Office you’re using?
Another option: Play in Click Sequence
Beginning with PowerPoint 2016, one more video playback option is available: Play in Click Sequence. With that option set, when you click anywhere on the slide to advance to the next step (or when you press the Spacebar, Right arrow key, or other key that advances to the next step), the video plays.
This is an improvement over PowerPoint 2013 and prior versions where, with the On Click option, you literally have to click the video to make the video play because other actions (such as pressing the Spacebar or the Right arrow key) don't cause the video to play.
See Play a video automatically or when clicked for more details about Play in Click Sequence.