How did the play, pause and stop icons become media symbols?

It's one of the world's most recognisable icons - used across languages, writing systems, and cultures. The single right-pointing triangle has become synonymous with the play function ... inherently suggesting the start of something. But how did it become the sign for play? Dr Jason Kennedy is a senior lecturer in the department of Animation, Visual Effects & Game Design at Auckland University of Technology and he's been looking into the history of other universal media symbols. He joins Jesse in the studio.