The iconic speech (video and audio) is owned by the king family and they will sue your black ass if you use it without buying a license first.
Think about it: you've never heard the whole speech have you. Even today, the media only played 10 second bumps bc they don't want to pay royalties.
The mlk family also demanded ( and got) hundreds of thousands of dollars to allow the mlk memorial to be built in DC.
I'm sure he'd be proud