Brown, 28, joined the Raiders as an undrafted free agent out of Boston College in 2006. After five seasons with the Raiders, Brown signed with the New England Patriots last year but was cut after the preseason. He then rejoined the Raiders, suiting up for three games in 2011 before he sustained a concussion and was placed on injured reserve for the third time in four seasons.
Brown, listed at 6-foot-2 and 235 pounds, has played in 58 career games and made 13 starts.
Blackstock, who played his college ball at Virginia, was a third-round draft pick of the Arizona Cardinals in 2005. He has played in 74 games, seven of them starts, in five NFL seasons with three teams -- the Cardinals, Cincinnati Bengals and Raiders. The 29-year-old has recorded 84 tackles, four sacks and a pair of forced fumbles. Blackstock is listed at 6-foot-3 and 245 pounds.
The Ravens also announced the signing of guard Cordaro Howard, who played 10 games, four of them starts, for the Buffalo Bills in 2010. He spent the entire 2011 season injured reserve.