doc/filters: note default for zoompan's duration

diff --git a/doc/filters.texi b/doc/filters.texi
index eb0a0b6a0bacceaab71440ff503eddc34a84d085..30dee5531db72a63489a7bc8373fabea8608e68d 100644 (file)
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -22170,7 +22170,7 @@ Set the x and y expression. Default is 0.
 @item d
 Set the duration expression in number of frames.
 This sets for how many number of frames effect will last for
-single input image.
+single input image. Default is 90.
 
 @item s
 Set the output image size, default is 'hd720'.