This week Google announced that the new default setting for videos in Google Slides is going to be automatic playback when presenting. The previous default was for videos to only play when you chose to play them while presenting. Now as soon as you advance to a slide that has a video in it the video will start playing. The new default playback will probably prove to be incredibly annoying to those of us who like to explain a bit about a video before we play it for our students or other audience.
Fortunately, you can change the playback setting for the videos that you insert into Google Slides. You can do that by highlighting the video in your slide and then opening the "format options" menu. In that menu you can change the video from the default automatic playback to manual playback.