Non You-Tube Video?
If it’s not a YouTube video, you have two choices. Upload the video to Youtube (this would be the best!) or follow this video’s instructions to mimic embedding a video into a google slide with an external link.
Since audio isn’t fully supported in Google Slides, if you want to embed audio, you have to do a workaround. This involves using a video with a blank graphic to act as an audio file. Watch the video below to learn how.