If your goal is to file a provisional patent application, describing the invention in a YouTube video does not have any positive consequences. The Patent Office does not award earlier filing dates or confer any patent rights on the basis of videos, publications, etc. The only way to receive patent rights is to file a patent application (either provisional or nonprovisional). In the U.S., there was formerly a rare process called "interference" which would arise when two people claimed the same invention in pending patent applications. In those cases, it could be helpful to have documentation of the date you conceived of the invention. However, I believe this process no longer exists under the AIA--you should confirm this with your patent counsel, and in the meantime, you can read more about it here.
However, in the U.S. (and in most systems around the world), describing your invention in a publicly accessible YouTube video will have extremely serious negative consequences. Let's start with the case of a video that is listed as "Public." As soon as you describe your invention in an electronic publication, it is now available as prior art for any patent application--even a patent application that you might file later. (To qualify as prior art, the video must have been published before the application was filed and before any "parent" application was filed.) For example, let's say I invent a new chair on Jan. 1, describe it in a publicly available YouTube video on Feb. 1, and then file my first patent application on Mar. 1. Once my patent application receives examination, the claims will be rejected in light of the YouTube video I created on Jan. 1. The fact that it's my video is inconsequential; this fact does not make my patent application immune to it.
So, to the question I think you're asking, I believe the short answer is: any video you create in attempts to exclude others from filing will also exclude you from filing.
You might be asking a separate question: "I want to share information about my invention and the best way to do that is in a video. My goal is not for the video to prevent others from filing. Rather, my goal is to distribute information in a controlled way only to select people I work with. I must prevent the information from reaching the public, as I plan to file a patent application. Can I do this in an unlisted YouTube video, or will the unlisted YouTube video become prior art which would then preclude any later-filed patent?"
I do not know enough case law to answer this question. But my suspicion is that unlisted YouTube videos would qualify as prior art for later-filed applications that do not predate the video through priority claims. There is a lot of case law involving things like conversations between friends at closed parties, websites that were accessible by link but weren't password protected, websites accessible only through a complex file system. It's a thorny field to navigate, and the advice of patent counsel in your jurisdiction is important.
Other sources you might want to read are here (start at second half of p. 3), here (section II), here, and here. Note that these relate to different countries/jurisdictions.
I am no expert, and this response is for informational purposes only and not for the purpose of providing legal advice. You should contact your attorney or legal expert to obtain advice with respect to any particular issue or problem. Laws can differ dramatically from country to country, state to state, and technology field to technology field.
