Google released a new feature today that allows users to insert videos hosted and stored in Google Drive, directly into a Google Slide.  So if you create a video for use in a presentation, you can save it in Google Drive, and easily add it to your presentation in just a few short steps.  You can also choose how much of the video clip is shown in the presentation, and choose from other settings as well.  

Also if you are in a school district that normally blocks the use of YouTube on campus, your students can utilize the option of downloading a video from YouTube, and saving it in Google Drive.  Then follow the simple steps shown in the video below to insert the video from Google Drive.  

Just make sure that if you are using videos from YouTube, or are downloading them that you cite your source by copying and sharing the URL in your Google Slide show.