Leonardo DiCaprio is getting right back to work on a new movie -- which makes sense, we suppose, since his Oscar campaign is finally done ... with nothing to show for it this year.

TMZ has obtained video of the actor on set Monday in Northern California, where he was in full-blown costume, makeup and character as he and Paul Thomas Anderson's crew shot a scene with at least a few different takes ... and LDC going all out while cameras were rolling.

As you can see here, Leo is taking on quite a different character than what he might normally do -- lately, the guy's been playing more historical figures in period pieces (see "Killers of the Flower Moon," "Once Upon a Time... in Hollywood," etc.).

Here, Leo looks like more of a modern down-on-his-luck dude in a setting that looks like present day. In fact, he comes across as kinda homely ... and rough around the edges.

He even puts his acting chops on display in our video ... yelling into the receiver at a payphone, slamming it and slumping down with a lot of emotion. Dude's very in his element.

No word yet on what the plot of this film might be -- it's being kept under wraps for now -- but we do know who else will eventually join Leo as the production continues ... Sean Penn and Regina Hall have also been tapped to star, so it's a solid cast in the mix here.

An eyewitness also tells us that it appears that the fictional town PTA and co. are trying to create might be called Baktin Cross ... 'cause the cop cars that pass feature that signage.

It's all still shrouded in mystery -- but knowing PTA's style, this looks to be shaping up in the vein of "Licorice Pizza," "Boogie Nights," "Inherent Vice," "Punch-Drunk Love" or even "Magnolia." Speaking of 'BN,' fun fact ... Paul has publicly said he wanted Leo for that lead role, but wasn't able to land him, going with Mark Wahlberg instead. LDC was the one who got away!

Now, he's finally got his chance to work with Leo ... and so far, it appears they're making magic onscreen. It's also not lost on us that PTA has gotten tons of actors nominated at the Oscars over the years ... including Tom Cruise, Joaquin Phoenix, Julianne Moore and others.

Seeing how Leo missed out this year for his Martin Scorsese flick, maybe he wants another bite at the apple with Paul. Based on what we see here ... the homeboy's coming for that statuette.