[exikyut]

You just made me think of a GIF-to-mp4 conversion service that runs as a proxy.

Sadly, because of the "HTTPS everywhere!!!11" thing, such a service would not be viable (it would need to rewrite the <img> to a <video> in order to work, of course).

[pjc50]

Opera were offering something like this for a while. With the support of a browser and HTTP proxying it's not a problem, the SSL terminates at the proxy and is re-encrypted under the proxy's SSL.

Many web services will take an uploaded gif and turn it to webm before showing it, e.g. Twitter.