Why has it taken so long to make a Martin Luther King film?

The new film Selma looks at the marches led by Dr Martin Luther King Jr in Alabama amid fierce opposition as he tried to secure the right of African Americans to vote freely.

The picture might have been viewed as a period film, but coming in the wake of two recent high profile cases in which African-American men died in interactions with white police officers the movie has gained great topicality.

Talking Movies' Tom Brook reports.