Video Aspect ratio

[ab190670]

Hi, is there a way when watching a video/film that has different aspect ratios to set it so that it changes as the size changes to fill the screen without cropping, im happy with black bars when the film don't fit the native 2:1 screen ratio but some documentaries ive watched that have multiple ratios some 2:1 some not and wondered if there was a setting i'm missing. hope this makes sense.
Thanks Andrew