Actually, it's Street Fighter III: 3rd Strike (lol). It probably looks like it because M.U.G.E.N. was greatly influenced by the SF series, after all.
Well I recognized the sprites immediately as SF III sprites. Anyone can recognize how big Chun Li's legs got in that addition. I asked because it looked like a video from M.U.G.E.N. Tournament 3 from a few years back, with the masses huddled around what looked like a large computer monitor.