Serena Williams' Wedding Video, Venus Shakes to 'Back That Ass Up'

Here it is ... the first footage from INSIDE Serena Williams' awesome New Orleans wedding -- with incredible dresses, the Cupid Shuffle ... and Venus Williams gettin' down to "Back That Ass Up!"

The party looked like a blast -- guests drinking and dancing while the DJ turned the party up!

Serena looked beautiful -- sporting a short princess style cocktail dress with white sparkly Nike shoes so she could dance comfortably.

Venus also looked smokin' hot in a tight fitting lace cocktail dress of her own.

We're told everyone had a GREAT time -- and the food was an absolute hit!!

One partygoer tells us there was a Cajun section, seafood section, a "Tour of Italy" section with all sorts of pasta ... a steak section with different cuts of meat and a traditional American section.

Who's hungry now!?!?