"Mercedes is a Princess"

Yesterday morning we were all sitting at the table, some of us eating breakfast, some of us not (fast sunday). Cooper started telling me something quite emphatically, and it took me a minute or two to figure out what he was saying. He kept saying, "Mercedes is a princess. Mercedes is a princess." I figured it out and realized what they'd been playing that morning. Mercedes is great at "giving directions" (code for being bossy) and Cooper is pretty good at following them. They love playing together.

So I tried to put a video of it here. Why does the sound not work? Does anyone know? It works fine on our computer in quick time, but won't transfer sound to the web or i movie. Help?