How to change output frame size?

Hello.

I have videofile 1920*1080. I have cropped it for other size (i.e. look on screenshot). And now i want to encode to the newfile. But after encoding i will get 1920*1080 video with black background. What should i do to make output frame as i crop? I mean (again look my screenshot) output videofile should be like vertical phone video and other frame size (600*1080 for example).

Please don't tell me about "proper" ratio for sides like 720*480, 1024*768 etc. My question not about that.