There's a Fediverse challenge which runs throughout June called AudioMo:

1. Create & post an audio file every day in June using the hashtag #AudioMo. It can be anything including music, speech, sounds, ambient recordings etc.

2. That's it!

Mastodon lets you post actual audio files, they don't need to be video. They can be any length as long as the file size is under 40 megabytes. Formats can be MP3, OGG, WAV, FLAC, OPUS, AAC, M4A or 3GP.

The challenge also has an account at @audiomo