Hi @Geordi Darby. Can you provide more details on what you are trying to do? Essentially in Stream, you can create a group for each department. Videos can then be permissioned to 1 or more groups, allowing your videos to only be visable by those who have permissions in the group.
Lets assume you have Group 1 which is a broader department in your organisation, and Group 2 which is a subset team of Group 1. When you upload a video, if you want everyone on Group 1 to have access, you can permission the video to just Group 1. If you want just Group 2 to have access then just permission the video to Group 2. Lets say that Group 3 includes a subset of Group 1 but also includes people from another department - in the case where you want everyone in Group 1 and Group 3 to have access, you would permission the video to Group 1 and 3. You can additionally give everyone in your company access to a video aswell.
