I have to write about WWII for my history class and we were required to use primary sources. I found a film used as propaganda back in the 1940s and would want to know if it can be considered a primary source? None of it was edited, it had no commentary at all. Just the film posted on YouTube. The user who posted it is I guess a professor but not one of those official accounts on YT.
I would have no particular concern, personally. The medium may not be the primary medium, but the source itself, I think, would meet the requirement of being a product of the time.
I wouldn't see this as being any different to emailing the National Archives (in the US) and asking for a copy of the document in Box A, Record Group 123, referencing whatever. They won't be sending you the original thing, but a photocopy of it, an electronically produced facsimile, sent into your hands by the mechanisms of modern times.
If you were to email the Archives today and place an order for a footage from WW2 not already digitized by them, they will instruct you (at great cost, I have discovered), to use an approved copying service, who will make two copies. One to send to you, and one for the Archives to keep to distribute to future folks. And, indeed, if you show up in person and ask to see the video, they may well provide you with the digitised copy to watch, as opposed to the (now fragile) original film, if a digitised copy already exists. So the 'principle' I would submit is validated.
As long as you are indeed fairly sure that it has not been edited in the upload process, I think it's fine. Even if it has been edited, it may still be usable, depending on what conclusion or fact you intend to support with it.
I might use it in a pinch, but would definitely note the caveat. You might try the internet archive for stuff like that as well if you haven’t already. You could also see if you can find an electronic copy of the script to match it up.