You can link a Brief Document Type to a Job Category. This will restrict which Document Types any User can see on a Brief created on that Job.
For example, a User creates a Job with a Category of Video, then a User who adds a brief to that Job will only have access to a specific set of predefined Brief Document Types.
Not only will you be able to link the Document Type but you will also be able to add custom fields to these Document Types. These additional fields will change to those associated with the Document Type selected.