Seems like it be highly useful for sites that do backend conversion. Never been a big fan of ruby but its cool seeing its uses.
I've gone ahead and slapped together APNG support, which not only cuts file sizes down; but conversion takes about 5 seconds for the largest MP4 I tested.
http://i.imgur.com/sCVBYC2.png This came out to be 9.9mb while its gif counterpart was too big to even upload; even with its quality cut.
https://github.com/space150/gifvine/blob/master/gifvine.rb
It runs server-side however, and requires several dependencies (ffmpeg, imagemagick) unlike JVine which runs client-side as a Java applet.