Use a media player
Add a Media Player from the room's creation tools. Search for a video or enter a supported video link, then play it. The room sees the same video. Move your pointer over the player, or tap it, to show its controls.
Show something from your browser
Try sharing a browser tab with audio enabled if your browser offers it.
Why is a movie black or silent?
Some streaming services protect their video, so a screen share can show a black picture or no sound. Here cannot guarantee that a particular streaming service can be shared. Try content that permits sharing or a supported video in the media player.
If nobody hears a shared tab, stop sharing and start again with the audio option enabled.