Transition To Video Options

[sonic4]

So you know how in older video games where, if you wait on a title screen long enough, you get a demo? I want to do that in CSS, however, i don't know how. Here's my @keyframes rule

@keyframes switch
{
from {background-image: url(images/titlescreen.gif)}
to {background-image: url(videos/commercial.mp4)}
}

Here's what I put in my body CSS (same sheet):

background-image: url(images/titlescreen.gif);
background-repeat: no-repeat;
background-size: cover;
animation-name: switch;
animation-duration: 10s;

IF this is impossible, then let me know.