You can't, sorry! I'm afraid we don't allow creating threads and posts for advertisement. You're welcome to put a link to your Youtube channel in your signature though
Yeah, signature, user title, your profile page, anywhere is fine except a dedicated thread.
Here's something sneaky you can do though (the mods always give me funny looks when I publicly share sneaky ideas) - if your video is about cats, for example, then make a thread in Brewster's Caf? about cats and include your video. Works with most videos, especially if you don't go around yelling "I own this video!"