(FYI discussion about audi/video is also ongoing here : https://github.com/YunoHost/issues/issues/1607#issuecomment-689026700 )
I apologize Aleks. I thought that audio/video works as @lps says in his reply, but the discussion in github says otherwise…
Not sure what issues others are having but it works for me.
I did notice that when using the Conversations app or in my case Pix Art Messenger (simplified fork) that it is not 100% stable. Meaning that the icons for phone and video sometimes go away. It usually just takes a re-authenticating between you and your contact, by removing and adding again.
So XMPP chat and file upload works for you? If so the video and audio should work as well. As far as I know they use the same Ports.
Are they open in your Diagnosis panel of Yunohost?