He's playing with the reed on the bottom. I only mentioned playing with it on top because it shows that double lip must have come before single lip. Possibly some current players of baroque clarinet or chalumeau might try having the reed on top, but I haven't heard of any examples so far.

Some classical players still use double lip, and you can find videos online advocating it- for example, the maker Tom Ridenour likes it and refers to it as French embouchure.

I don't know what proportion of jazz players use double lip. I do use it myself and find single lip awkward.

I've watched that video before, I didn't realise he was playing with the reed on top! I thought double lip was still with the reed in the normal position, on the bottom.

info says benny changed to double lip in the early 50,s  tho i dont see why.

Double lip embouchure is the way the clarinet was played when it was invented in the 1700s. It was also common to play with the mouthpiece rotated so the reed was on top, for which a single lip embouchure is impossible. Playing with the reed on top was mostly abandoned in the 1800s, although some Italian players continued doing it until the early 1900s. Also in the 1800s, the German player Klose advocated using a single lip embouchure instead of double lip, and most players worldwide gradually switched to it. A summary of the history can be found here:

https://clarinetcorner.wordpress.com/2013/05/05/mouthpiece-puzzle/

Some classical players still use double lip, and you can find videos online advocating it- for example, the maker Tom Ridenour likes it and refers to it as French embouchure.

I don't know what proportion of jazz players use double lip. I do use it myself and find single lip awkward.

I notice that classical players hold the instrument almost vertical, because of the way a reed instrument works. But jazz players tend to be portrayed holding it more horizontal. But when I do this the sound is weaker because the reed is being blown at a different angle due to the classic clarinet embouchure.
I know many players favour the double lip embouchure and this allows the player to hold the instrument higher. So is that where it comes from, the new orleans jazz era?