The desire for clean cheap energy is so great that some people take advantage of peoples desires and this is what you end up with, charlatans who come up with gadgets that supposedly break the law of conservation of energy.
It takes energy to break the hydrogen-oxygen covalent bond, about 9.95eV to break both bonds. There is no magic way of breaking this bond which takes less energy than the normal 9.95eV of energy. It actually takes more energy, because of inefficiencies in any system, to break the covalent bond than the energy you get back by reforming that bond...although technically it takes the same energy to break that bond that is returned when the bond is formed. If that makes any sense.
What the video is showing is a chemical process, not a subatomic process. Only at the subatomic level will you find mass being converted to energy or the reverse, which is clearly not the case here.
My guess is that what he is doing is bombarding the water with enough electromagnetic energy to break those bonds thus releasing hydrogen and oxygen...what you are seeing is the energy released when those bonds reform. I don't know how it does not affect a human standing next to it. Either that or it has something to do with separating the sodium and chlorine ions outside of the solution and seeing the heat formed as they form back into table salt. I'm sure some chemist somewhere has figured out what is actually happening.
Conservation of energy - Wikipedia, the free encyclopedia