How do you turn a 12-page script into a 78-minute comedy?
The prolific indie director Joe Swanberg ("Drinking Buddies") did it in "Happy Christmas" by picking good actors who have astonishing improv skills.
It also helps to cast your own two-year-old. Swanberg cast his son Jude to play the son of Jeff, a filmmaker played by Swanberg.
The movie -- screening in the U.S. Dramatic competition of the 2014 Sundance Film Festival -- centers on a Christmas season in which Jeff and his novelist wife Kelly (Melanie Lynskey) play host to Jeff's sister Jenny (Anna Kendrick), who's emotionally messed up after a recent break-up.