If @is_letterbox is true, then the value specifies the
last line of a horizontal letterbox bar area at top of reconstructed frame.
Otherwise, it specifies the last horizontal luminance sample of a vertical pillarbox
bar area at the left side of the reconstructed frame
If @is_letterbox is true, then the value specifies the last line of a horizontal letterbox bar area at top of reconstructed frame. Otherwise, it specifies the last horizontal luminance sample of a vertical pillarbox bar area at the left side of the reconstructed frame