Normally I would embed a gif like so.
<img src="http://i.imgur.com/awHPuBp.gifv">
Although I get an error that the image could not be loaded.
I'm just wondering what mark up I will need to use so that I can display the GIFV.
GIFV is created by imgur and more information can be found here.
I just checked that demo site. It seems that they just convert the video to a webm video (in case of Firefox). Check this file here which comes from the demo: http://i.imgur.com/A61SaA1.webm
So I would say you could also just use the <video> tag to embedd those "gif" files. I just guess that use a feature detection and a video converting logic. No idea what this nonsense should be for.