Quantisation offset.
Must be set to the size of this data structure (that is, sizeof(AVRegionOfInterest)).
Distance in pixels from the top edge of the frame to the top and bottom edges and from the left edge of the frame to the left and right edges of the rectangle defining this region of interest.
Structure describing a single Region Of Interest.
When multiple regions are defined in a single side-data block, they should be ordered from most to least important - some encoders are only capable of supporting a limited number of distinct regions, so will have to truncate the list.
When overlapping regions are defined, the first region containing a given area of the frame applies.