@table @option
@item x
@item y
-Specify the top left corner coordinates of the box. Default to 0.
+The expressions which specify the top left corner coordinates of the box. Default to 0.
@item width, w
@item height, h
-Specify the width and height of the box, if 0 they are interpreted as
+The expressions which specify the width and height of the box, if 0 they are interpreted as
the input width and height. Default to 0.
@item color, c
video with inverted luma.
@item thickness, t
-Set the thickness of the box edge. Default value is @code{3}.
+The expression which sets the thickness of the box edge. Default value is @code{3}.
+
+See below for the list of accepted constants.
+@end table
+
+The parameters for @var{x}, @var{y}, @var{w} and @var{h} and @var{t} are expressions containing the
+following constants:
+
+@table @option
+@item dar
+The input display aspect ratio, it is the same as (@var{w} / @var{h}) * @var{sar}.
+
+@item hsub
+@item vsub
+horizontal and vertical chroma subsample values. For example for the
+pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.
+
+@item in_h, ih
+@item in_w, iw
+The input width and height.
+
+@item sar
+The input sample aspect ratio.
+
+@item x
+@item y
+The x and y offset coordinates where the box is drawn.
+
+@item w
+@item h
+The width and height of the drawn box.
+
+@item t
+The thickness of the drawn box.
+
+These constants allow the @var{x}, @var{y}, @var{w}, @var{h} and @var{t} expressions to refer to
+each other, so you may for example specify @code{y=x/dar} or @code{h=w/dar}.
+
@end table
@subsection Examples
@example
drawbox=x=10:y=10:w=100:h=100:color=pink@@0.5:t=max
@end example
+
+@item
+Draw a 2-pixel red 2.40:1 mask:
+@example
+drawbox=x=-t:y=0.5*(ih-iw/2.4)-t:w=iw+t*2:h=iw/2.4+t*2:t=2:c=red
+@end example
@end itemize
@section drawgrid
@table @option
@item x
@item y
-Specify the coordinates of some point of grid intersection (meant to configure offset). Both default to 0.
+The expressions which specify the coordinates of some point of grid intersection (meant to configure offset). Both default to 0.
@item width, w
@item height, h
-Specify the width and height of the grid cell, if 0 they are interpreted as the
+The expressions which specify the width and height of the grid cell, if 0 they are interpreted as the
input width and height, respectively, minus @code{thickness}, so image gets
framed. Default to 0.
to color name after @@ sign.
@item thickness, t
-Set the thickness of the grid line. Default value is @code{1}.
+The expression which sets the thickness of the grid line. Default value is @code{1}.
+
+See below for the list of accepted constants.
+@end table
+
+The parameters for @var{x}, @var{y}, @var{w} and @var{h} and @var{t} are expressions containing the
+following constants:
+
+@table @option
+@item dar
+The input display aspect ratio, it is the same as (@var{w} / @var{h}) * @var{sar}.
+
+@item hsub
+@item vsub
+horizontal and vertical chroma subsample values. For example for the
+pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.
+
+@item in_h, ih
+@item in_w, iw
+The input grid cell width and height.
+
+@item sar
+The input sample aspect ratio.
+
+@item x
+@item y
+The x and y coordinates of some point of grid intersection (meant to configure offset).
+
+@item w
+@item h
+The width and height of the drawn cell.
+
+@item t
+The thickness of the drawn cell.
+
+These constants allow the @var{x}, @var{y}, @var{w}, @var{h} and @var{t} expressions to refer to
+each other, so you may for example specify @code{y=x/dar} or @code{h=w/dar}.
+
@end table
@subsection Examples
@example
drawgrid=width=100:height=100:thickness=2:color=red@@0.5
@end example
+
+@item
+Draw a white 3x3 grid with an opacity of 50%:
+@example
+drawgrid=w=iw/3:h=ih/3:t=2:c=white@@0.5
+@end example
@end itemize
@anchor{drawtext}
position of the text. They can be either positive or negative
values. Default value for both is "0".
+@item start_number
+The starting frame number for the n/frame_num variable. The default value
+is "0".
+
@item tabsize
The size in number of spaces to use for rendering the tab.
Default value is 4.
@item mode
Set the matching mode or strategy to use. @option{pc} mode is the safest in the
-sense that it wont risk creating jerkiness due to duplicate frames when
+sense that it won't risk creating jerkiness due to duplicate frames when
possible, but if there are bad edits or blended fields it will end up
outputting combed frames when a good match might actually exist. On the other
hand, @option{pcn_ub} mode is the most risky in terms of creating jerkiness,