Ah. Thank you both. I never thought about podcasts. Of course, the pages I looked at don't use the term "Origin," so it's no surprise that I didn't make the connection. Don't have any, but don't want to be using that field in case I do get some.
Yes, I found Media Type, and was figuring on that as a likely option if "Origin" didn't work, so that's the direction I'll go.