• Find the mp4 file you want to include in your slide in your Google Drive.
  • Take a screenshot (Click on it in your drive to bring up a preview window and then Shift-Command-4) of the video to serve as a hyperlink placeholder to your mp4 file.
  • Go back to Google Slides, and find the slide you want to add the video link to.
  • Insert the screenshot you just took.
  • Downsize the screenshot as you see fit for your slide.
  • Select the screenshot and insert the hyperlink.
  • You can do this with CTRL + K (on a PC) or Command + K (on a Mac).
  • Paste the shareable link of the mp4 file in Google Drive.
  • Click Apply once you’ve pasted your link.
  • Now, your image is hyperlinked to take the user to the video located in Drive.

Here's the video that explains it.