How do I get out of sequencer mode/ black bars on the screen

How do i get rid of the black bars that are appearing on the top and bottom of the screen?
(They also show up while playing in preview and the launch mode.)

Just press that top button called Prespective at the corner:

108697-screen+shot+2016-09-28+at+6.53.23+am.png

And choose the Default Viewport at the end of the list, using Cinematic viewport, will bring bars back.

108698-screen+shot+2016-09-28+at+6.55.13+am.png

Or you just toggle with (Shift+D) and (Shift+C)

-m

Thanks man, appreciate the nice and precise answer. Hope original poster will remember to accept your answer.