There are a couple of ways you can deal with timing.
Fired as media plays. Updates every 250ms. Used to differ between browsers, but has now been standardised.
Unless you tell it otherwise expect Popcorn to 'sample' at that rate.
window.requestAnimationFrame tells the browser that you wish to perform an animation and requests that the browser schedule a repaint of the window for the next animation frame. The method takes as an argument a callback to be invoked before the repaint. https://developer.mozilla.org/en-US/docs/DOM/window.requestAnimationFrame