“audio ads are designed for videos where audience members may only be glancing at the screen occasionally, or might be ignoring the visuals altogether. To be clear, these ads won’t be audio-only, but YouTube says the audio should be doing most of the communication, while the visual side is limited to “a still image or simple animation.”
https://techcrunch.com/2020/11/17/youtube-targets-music-fans-with-new-audio-ad-format
