I work for a man who has invented an "improvement" to a skateboard. He put a video on YouTube a little over a year ago, but in the video all he does is ride the skateboard as part of an "art film" involving wind-surfing. There is no "discussion", no "teaching", nothing definitive about the design of the board. Can that be considered Prior Art?
This is currently an unsettled point, so it is impossible to give a good answer.
Intuitively, it seems that the second video you mention should be prior art, since it's a clear record of the invention. It would be arbitrary for a disclosure by video to make the disclosure exempt from being cited.
However, in Diomed, Inc. v. Angiodynamics, 450 F.Supp.2d 130 (D. Mass. 2006), a video was held not to be a printed publication, since there was no paper component to the video. This suggests that a video alone may not be enough, even if it shows all the necessary details.
I am not so aware of how US patent office would entertain the you-tube video, but my understanding of European Patent Law system, there is a provision that allow prior disclosure by any means to be used as prior art. For instance in the case T952/92, it clearly states "novelty of a claimed invention is destroyed by the prior disclosure (by any means) of an embodiment which falls within the claim. The possibility of a complete analysis of a prior sold product is not necessary." So whether a person skilled in art has done detailed analysis of a public disclosure is irrelevant as long as skilled person in that field could analyse the disclosure and develop the same improvement.