JoVE is an interesting resource - its a video platform, but it is also considered a journal. Consult your preferred style guide and cite this resource like you would an article in an electronic journal.
Welstead, G. G., Brambrink, T., Jaenisch, R. Generating iPS Cells from MEFS through Forced Expression of Sox-2, Oct-4, c-Myc, and Klf4. J. Vis. Exp. (14), e734, doi:10.3791/734 (2008).