The 26-year-old Ernster had been released by the Steelers at the end of training camp after losing a preseason battle for the punter's position with Berger.
Berger, 36, was signed in training camp to compete with Ernster for the punting job when Daniel Sepulveda suffered a torn ACL in training camp.
Berger averaged 41.9 yards per punt, but had seen his average decrease in recent weeks as he struggled with a hamstring injury in his left (non-kicking) leg.
Ernster has appeared in 19 games in parts of four NFL seasons. He averaged 41.7 yards per punt with Denver in 2006, the only season in which he spent the entire year on a team's roster.