diff --git a/DOCS/tech/vop.txt b/DOCS/tech/vop.txt
index 12906a8e8a..6ce72e49b7 100644
--- a/DOCS/tech/vop.txt
+++ b/DOCS/tech/vop.txt
@@ -62,7 +62,8 @@ Current plugins:
 	note: if -zoom is used, and underlaying filters (including libvo)
 	uncapable of scaling, then it defaults to d_width/d_height !
 	note 2: w/h values -1 means original width/height, 0 means scaled
-	d_width/d_height
+	d_width/d_height. -2/-3 means calculating w or h using the other
+	dimension and the original (-3) or prescaled (-2) aspect ratio.
     MPI: TEMP, accepts stride
     Special: dec_video and mpcodecs core autoloads it for colorspace conv.