Still can't quite get live format switch working

Format conversion is fine and working on the live server. However, many
times all that happens is that a blank window is sent to the client, and
only on refresh does the message appear (in mp4 format).

Still some work to do to get this done, so I've gone back to straight
gifs, although mashabout is saving them all in the background and will
attempt to swap the format if the gif has been used before. I'll see how
that goes while working out how to proceed.