Moderators should be able to adjust the volume of other speakers

[robertlong]

Moderators should be able to adjust volume of other speakers (including a “mute everyone else” button)

[jakewb-b]

I think there are potentially three interactions, that need separate UI for each:

1. Mute everybody except me
2. Mute an individual user (covered under https://github.com/vector-im/matrix-video-chat/issues/124)
3. Adjust the volume of an individual user

I am assuming that the intent of no3 is that, as a moderator making that adjustment, the change is felt by all users on the call? There is potentially a separate, lower priority, story where a non-moderator user can adjust individual users' volumes in a way that only affects them.

[heyakyra]

Relatedly, I would say they should also be able to:

• Enforce push-to-talk https://github.com/element-hq/element-call/issues/202
• Screen unapproved callers https://github.com/element-hq/element-call/issues/174
• Set view-only mode https://github.com/element-hq/element-call/issues/223