Use graphic files that have been saved as jpg. This format works on all computers and devices.
Audio files such as .mp3 cannot be inserted into Slides, Forms, or Sites. They must be prepared as movie files.
Movie files can be inserted directly from Google Drive only into Slides. If you want to insert movie files into a Form or into a site, they must be uploaded to YouTube first. You can then embed the movie files into a Form or Site.