Angela Watercutter at Wired writes:
Sometimes bad actors can do good accents. Sometimes great actors do terrible ones. In the video here, dialect coach Erik Singer analyzes the accents of 32 different actors to see who aces the accent test. Turns out, Idris Elba is one of greatest around. From his performance as Nelson Mandela in Mandela: Long Walk to Freedom to his mastery of the Baltimore accent in The Wire, he’s amazing. But he’s rare. Actors ranging from Brad Pitt to Will Smith have struggled with their ability to sound like they’re from somewhere else. Watch Singer analyze the best (and worst) in the biz above.
The sixteen minutes go by quickly, in efficient bite-sized analyses; if you have any interest in the subject, check it out.