What is the antonym for audiovisual?

There aren't any. 'Audio' is sound or music, so the only thing would be 'no audio', 'no sound' or 'no music'.

You could argue that mute(d) is an antonym, but it is not really used commonly.

For example, these versions of a sentence:

• A - There was no audio.
• B - It was mute.

Sentence 'B' does not make any sense, but it is considered to be an antonym anyway.