Once done, customize the font, size, and background for better readability ... No, an internet connection is required for PowerPoint’s live captions and subtitles feature to function.

You can change the background to anything you like if you're using Powerpoint to create presentations: a picture, a color, a gradient, or even an in-motion video. You'll know the best background ...

Launch Microsoft PowerPoint, and open the PPTX file for which you want to use a GIF as the background. Select the appropriate slide. Click the "Design" tab, and locate the "Background" section.