The video shows hot air around a soldering iron.
Inexpensive schlieren video technique using sensor dead space as a grid,
Robert B. Teese and Matthew M. Waters,
Optical Engineering, Volume 43, Issue 11, pp. 2501-2502, November 2004.
You can use this technique to do it yourself.Matt Waters has also published a short book about the method.
Links for more information about schlieren photography:
SCHLIEREN PHOTOGRAPHY PRINCIPLES by Andrew Davidhazy
SCHLIEREN AND SHADOWGRAPH TECHNIQUES: VISUALIZING PHENOMENA IN TRANSPARENT MEDIA, by Gary S. Settles
Schlieren Images by Loren Winters
Schlieren Photographs by J. Kim Vandiver
Copyright 2004, RIT