@@ -1546,8 +1546,38 @@ approach is yet to be tested.

 Add paddings to the input image, and places the original input at the

 given coordinates @var{x}, @var{y}.

-It accepts the following parameters:

-@var{width}:@var{height}:@var{x}:@var{y}:@var{color}.

+This filter accepts the following parameters:

+

+@table @option

+@item width, height

+

+Specify the size of the output image with the paddings added. If the

+value for @var{width} or @var{height} is 0, the corresponding input size

+is used for the output.

+

+The @var{width} expression can reference the value set by the

+@var{height} expression, and vice versa.

+

+The default value of @var{width} and @var{height} is 0.

+

+@item x, y

+

+Specify the offsets where to place the input image in the padded area

+with respect to the top/left border of the output image.

+

+The @var{x} expression can reference the value set by the @var{y}

+expression, and vice versa.

+

+The default value of @var{x} and @var{y} is 0.

+

+@item color

+

+Specify the color of the padded area, it can be the name of a color

+(case insensitive match) or a 0xRRGGBB[AA] sequence.

+

+The default value of @var{color} is "black".

+

+@end table

 The parameters @var{width}, @var{height}, @var{x}, and @var{y} are

 expressions containing the following constants:

@@ -1582,46 +1612,13 @@ horizontal and vertical chroma subsample values. For example for the

 pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.

 @end table

-Follows the description of the accepted parameters.

-

-@table @option

-@item width, height

-

-Specify the size of the output image with the paddings added. If the

-value for @var{width} or @var{height} is 0, the corresponding input size

-is used for the output.

-

-The @var{width} expression can reference the value set by the

-@var{height} expression, and vice versa.

-

-The default value of @var{width} and @var{height} is 0.

-

-@item x, y

-

-Specify the offsets where to place the input image in the padded area

-with respect to the top/left border of the output image.

-

-The @var{x} expression can reference the value set by the @var{y}

-expression, and vice versa.

-

-The default value of @var{x} and @var{y} is 0.

-

-@item color

-

-Specify the color of the padded area, it can be the name of a color

-(case insensitive match) or a 0xRRGGBB[AA] sequence.

-

-The default value of @var{color} is "black".

-

-@end table

-

 Some examples follow:

 @example

 # Add paddings with color "violet" to the input video. Output video

 # size is 640x480, the top-left corner of the input video is placed at

 # column 0, row 40.

-pad=640:480:0:40:violet

+pad=width=640:height=480:x=0:y=40:color=violet

 # pad the input to get an output with dimensions increased bt 3/2,

 # and put the input video at the center of the padded area

@@ -37,6 +37,8 @@

 #include "libavutil/imgutils.h"

 #include "libavutil/parseutils.h"

 #include "libavutil/mathematics.h"

+#include "libavutil/opt.h"

+

 #include "drawutils.h"

 static const char *const var_names[] = {

@@ -93,14 +95,16 @@ static int query_formats(AVFilterContext *ctx)

 }

 typedef struct {

+    const AVClass *class;

     int w, h;               ///< output dimensions, a value of 0 will result in the input size

     int x, y;               ///< offsets of the input area with respect to the padded area

     int in_w, in_h;         ///< width and height for the padded input video, which has to be aligned to the chroma values in order to avoid chroma issues

-    char w_expr[256];       ///< width  expression string

-    char h_expr[256];       ///< height expression string

-    char x_expr[256];       ///< width  expression string

-    char y_expr[256];       ///< height expression string

+    char *w_expr;           ///< width  expression string

+    char *h_expr;           ///< height expression string

+    char *x_expr;           ///< width  expression string

+    char *y_expr;           ///< height expression string

+    char *color_str;

     uint8_t color[4];       ///< color expressed either in YUVA or RGBA colorspace for the padding area

     uint8_t *line[4];

@@ -111,18 +115,8 @@ typedef struct {

 static av_cold int init(AVFilterContext *ctx, const char *args)

 {

     PadContext *pad = ctx->priv;

-    char color_string[128] = "black";

-

-    av_strlcpy(pad->w_expr, "iw", sizeof(pad->w_expr));

-    av_strlcpy(pad->h_expr, "ih", sizeof(pad->h_expr));

-    av_strlcpy(pad->x_expr, "0" , sizeof(pad->w_expr));

-    av_strlcpy(pad->y_expr, "0" , sizeof(pad->h_expr));

-    if (args)

-        sscanf(args, "%255[^:]:%255[^:]:%255[^:]:%255[^:]:%255s",

-               pad->w_expr, pad->h_expr, pad->x_expr, pad->y_expr, color_string);

-

-    if (av_parse_color(pad->color, color_string, -1, ctx) < 0)

+    if (av_parse_color(pad->color, pad->color_str, -1, ctx) < 0)

         return AVERROR(EINVAL);

     return 0;

@@ -413,6 +407,26 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)

     return ff_filter_frame(inlink->dst->outputs[0], out);

 }

+#define OFFSET(x) offsetof(PadContext, x)

+#define FLAGS AV_OPT_FLAG_VIDEO_PARAM

+static const AVOption options[] = {

+    { "width",  "Output video width",       OFFSET(w_expr),    AV_OPT_TYPE_STRING, { .str = "iw" },    .flags = FLAGS },

+    { "height", "Output video height",      OFFSET(h_expr),    AV_OPT_TYPE_STRING, { .str = "ih" },    .flags = FLAGS },

+    { "x",      "Horizontal position of the left edge of the input video in the "

+        "output video",                     OFFSET(x_expr),    AV_OPT_TYPE_STRING, { .str = "0"  },    .flags = FLAGS },

+    { "y",      "Vertical position of the top edge of the input video in the "

+        "output video",                     OFFSET(y_expr),    AV_OPT_TYPE_STRING, { .str = "0"  },    .flags = FLAGS },

+    { "color",  "Color of the padded area", OFFSET(color_str), AV_OPT_TYPE_STRING, { .str = "black" }, .flags = FLAGS },

+    { NULL },

+};

+

+static const AVClass pad_class = {

+    .class_name = "pad",

+    .item_name  = av_default_item_name,

+    .option     = options,

+    .version    = LIBAVUTIL_VERSION_INT,

+};

+

 static const AVFilterPad avfilter_vf_pad_inputs[] = {

     {

         .name             = "default",

@@ -438,6 +452,7 @@ AVFilter avfilter_vf_pad = {

     .description   = NULL_IF_CONFIG_SMALL("Pad input image to width:height[:x:y[:color]] (default x and y: 0, default color: black)."),

     .priv_size     = sizeof(PadContext),

+    .priv_class    = &pad_class,

     .init          = init,

     .uninit        = uninit,

     .query_formats = query_formats,