Open Broadcaster Software®️ | OBS
Open source tool for live mixing video streaming. You can put a text overlay on top of a video, for example. You can also set up different scenes in advance so you can transition between different combos. This also has an audio mixer so you can adjust the volume between a shared video and your own microphone (or other inputs). It's compatible with other platforms, so you can use it with Zoom or whatever you're currently using for video conferencing or streaming.