volume_entity can be used to designate a separate media_player for your volume control. This release adds the remote.* domain to use as volume_entity. Use this in setups (e.g.: Apple Tv connected to receiver via CEC) where the traditional volume control does not work and comes with an associated remote.* entity.
Example
type: custom:yet-another-media-player
entities:
- entity_id: media_player.living_room_apple_tv
volume_entity: remote.living_room_apple_tv