Add more fields to content type dynamically I am looking for the ability to let the user who is creating the page add more fields to the node rather than the entire content type.

For example if I had a content type called Book and each content type I wanted the user to select how many authors the book had. Some books might have 5-50 authors. It does not make sense to be to create 50 fields in the content type, id rather let the user select how many author fields they will need with an "add more" button.

In my case I am using videos and the Brightcove video module that adds a custom field to my content types. I figured the process would be the same. What is the best way to create this add more experience?
This is in core for the field types supported by the fields module.  When you add the field to the node type, just pick Unlimited  as the maximum number of values the user can enter for this field.  Every time the user adds a field, a new one ready to be filled in will appear.