Audio visual NFTs are mixed media artworks that can be collected on SuperRare.co.

https://superrare.co/artwork-v2/first-contact-16208

They can be the created by a single artist producing both visual and audio materials but also as collaborations between a visual artist and a sound artist.

https://superrare.co/artwork-v2/star-crossed-14547

In a given artwork, there's often an emphasis on either the audio or visual aspect.

• For musicians, audio + visual pieces can be thought of as the evolution of the album cover.
• For visual artists an audio element can be used to reinforce the message or emotion expressed by the visual media.

https://superrare.co/artwork-v2/elephant-dreams-14316