Off-topic: Strangely enough, it reported the same size for the MP4, but downloading it [0] shows that it's 1.1 MB. Inspecting it with `mediainfo` shows that it was encoded with the Baseline Profile, so that might explain the counterintuitively large size. (This profile is used for supporting low-powered devices, like phones, and results in a higher bitrate being used; 757 vs 252 Kbps in this case.) It seems that Gfycat just reports the WebM size either out of technical constraints, and/or for the sake of boasting higher amounts of bandwidth saved.