HTML5 fallback images are being loaded by the browser, even though HTML5 video is supported

Question

I have some HTML5 videos with animated GIFs as fallback. Sadly, the GIFs are being loaded even though HTML5 video is supported.

Without using javascript, is

Answer 1

I never found an answer to this, so I simply changed src to data-src on the fallback GIFs, and if IE8 or earlier was detected I changed it back to src using javascript.