It's a common usecase to request a video size after crop. Before
this patch, user must know the video size before crop, then set
crop_right/crop_bottom accordingly. Since HEVC can have different
CTU size, it's not easy to get/deduce the video size before crop.
With the new width/height options, there is no such requirement.
Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>