"The First International Modern Style" by Paul Greenhalgh
Art Nouveau by Green Frog
A nice selection of stills, including diverse examples of different arts from across Europe. With a brief, correct explanation of what Art Nouveau is.
Produced by Green Frog Productions and Folded Wing Enterprises and uploaded to YoutTube by "greenfrog40"
Art Nouveau 2
Henry van de Velde 2013
Video available in German