After some research i can say that i know what is the first nintendo related video uploaded to youtube.
Most people think that it's "Nintendo Show" uploaded by gslin on the 17th June 2005 : Nintendo Show – YouTube
This video is the 197th ever uploaded to the site and it's not the oldest nintendo video of youtube. It's the oldest Nintendo video that is still available to this day. But 3 days prior to Nintendo Show, the channel "Kazze" released "E3 Wii Line", one month after E3 2005, where the wii was announced. This video was deleted, but we still have the link thanks to an archive of Kazze's channel : http://www.youtube.com/watch?v=zkuUj_juYeA / YouTube – Kazze's Channel (archive.org)
But the video is not lost media ! Thanks to the website "Youtube Video Finder" we can download the video : https://web.archive.org/web/2oe_/http://wayback-fakeurl.archive.org/yt/zkuUj_juYeA
The video can be viewved with apps like VLC.
So don't hesitate to download the first nintendo video, uploaded the 14th of June 2005 by Kazze, the 103rd oldest youtube video.
by MMV_iceberg