gifv is actually webm and mp4 video format and plays via an swf player.
I've used the following bbcode to make it work on certain phpBB forums but have yet to make it resize dynamically for smaller screen sizes. Imgur's implementation also includes some Javascript which I did not bother with.
Code:
[gifv]{SIMPLETEXT1}://i.imgur.com/{SIMPLETEXT2}.gifv[/gifv]
Replacement:
Code:
<div style="width:100%; max-width:100%"><video poster="//i.imgur.com/{SIMPLETEXT2}.jpg" preload="auto" autoplay="autoplay" muted="muted" loop="loop" webkit-playsinline="" style="width: 916px; height: 390px;">
<source src="//i.imgur.com/{SIMPLETEXT2}.webm" type="video/webm">
<source src="//i.imgur.com/{SIMPLETEXT2}.mp4" type="video/mp4">
<object style="width: 100%" type="application/x-shockwave-flash" data="//s.imgur.com/include/flash/gifplayer.swf?imgur_video={SIMPLETEXT1}://i.imgur.com/{SIMPLETEXT2}.mp4&imgur_width=100%&imgur_url=">
<param name="movie" value="//s.imgur.com/include/flash/gifplayer.swf?imgur_video={SIMPLETEXT1}://i.imgur.com/{SIMPLETEXT2}.mp4&imgur_width=100%">
<param name="allowscriptaccess" value="never">
<param name="flashvars" value="width=100%">
<param name="width" value="100%">
<param name="version" value="0">
<param name="scale" value="scale">
<param name="salign" value="tl">
<param name="wmode" value="opaque">
</object>
</video></div>