@@ -1004,13 +1004,33 @@ can be used to test the monowhite pixel format descriptor definition.

 Scale the input video to @var{width}:@var{height} and/or convert the image format.

-For example the command:

+The parameters @var{width} and @var{height} are expressions containing

+the following constants:

-@example

-./ffmpeg -i in.avi -vf "scale=200:100" out.avi

-@end example

+@table @option

+@item E, PI, PHI

+the corresponding mathematical approximated values for e

+(euler number), pi (greek PI), phi (golden ratio)

+

+@item in_w, in_h

+the input width and heigth

+

+@item iw, ih

+same as @var{in_w} and @var{in_h}

-will scale the input video to a size of 200x100.

+@item out_w, out_h

+the output (cropped) width and heigth

+

+@item ow, oh

+same as @var{out_w} and @var{out_h}

+

+@item a

+input display aspect ratio, same as @var{iw} / @var{ih}

+

+@item hsub, vsub

+horizontal and vertical chroma subsample values. For example for the

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

+@end table

 If the input image format is different from the format requested by

 the next filter, the scale filter will convert the input to the

@@ -1025,6 +1045,36 @@ ratio of the input image.

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

+Some examples follow:

+@example

+# scale the input video to a size of 200x100.

+scale=200:100

+

+# scale the input to 2x

+scale=2*iw:2*ih

+# the above is the same as

+scale=2*in_w:2*in_h

+

+# scale the input to half size

+scale=iw/2:ih/2

+

+# increase the width, and set the height to the same size

+scale=3/2*iw:ow

+

+# seek for Greek harmony

+scale=iw:1/PHI*iw

+scale=ih*PHI:ih

+

+# increase the height, and set the width to 3/2 of the height

+scale=3/2*oh:3/5*ih

+

+# increase the size, but make the size a multiple of the chroma

+scale="trunc(3/2*iw/hsub)*hsub:trunc(3/2*ih/vsub)*vsub"

+

+# increase the width to a maximum of 500 pixels, keep the same input aspect ratio

+scale='min(500\, iw*3/2):-1'

+@end example

+

 @anchor{setdar}

 @section setdar

@@ -27,7 +27,7 @@

 #define LIBAVFILTER_VERSION_MAJOR  1

 #define LIBAVFILTER_VERSION_MINOR 77

-#define LIBAVFILTER_VERSION_MICRO  0

+#define LIBAVFILTER_VERSION_MICRO  1

 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \

                                                LIBAVFILTER_VERSION_MINOR, \

@@ -24,10 +24,40 @@

  */

 #include "avfilter.h"

+#include "libavutil/avstring.h"

+#include "libavutil/eval.h"

 #include "libavutil/pixdesc.h"

 #include "libavutil/avassert.h"

 #include "libswscale/swscale.h"

+static const char *var_names[] = {

+    "PI",

+    "PHI",

+    "E",

+    "in_w",   "iw",

+    "in_h",   "ih",

+    "out_w",  "ow",

+    "out_h",  "oh",

+    "a",

+    "hsub",

+    "vsub",

+    NULL

+};

+

+enum var_name {

+    VAR_PI,

+    VAR_PHI,

+    VAR_E,

+    VAR_IN_W,   VAR_IW,

+    VAR_IN_H,   VAR_IH,

+    VAR_OUT_W,  VAR_OW,

+    VAR_OUT_H,  VAR_OH,

+    VAR_A,

+    VAR_HSUB,

+    VAR_VSUB,

+    VARS_NB

+};

+

 typedef struct {

     struct SwsContext *sws;     ///< software scaler context

     struct SwsContext *isws[2]; ///< software scaler context for interlaced material

@@ -44,6 +74,9 @@ typedef struct {

     int slice_y;                ///< top of current output slice

     int input_is_pal;           ///< set to 1 if the input format is paletted

     int interlaced;

+

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

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

 } ScaleContext;

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

@@ -51,9 +84,12 @@ static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)

     ScaleContext *scale = ctx->priv;

     const char *p;

+    av_strlcpy(scale->w_expr, "iw", sizeof(scale->w_expr));

+    av_strlcpy(scale->h_expr, "ih", sizeof(scale->h_expr));

+

     scale->flags = SWS_BILINEAR;

     if (args) {

-        sscanf(args, "%d:%d", &scale->w, &scale->h);

+        sscanf(args, "%255[^:]:%255[^:]", scale->w_expr, scale->h_expr);

         p = strstr(args,"flags=");

         if (p) scale->flags = strtoul(p+6, NULL, 0);

         if(strstr(args,"interl=1")){

@@ -62,14 +98,6 @@ static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)

             scale->interlaced=-1;

     }

-    /* sanity check params */

-    if (scale->w <  -1 || scale->h <  -1) {

-        av_log(ctx, AV_LOG_ERROR, "Size values less than -1 are not acceptable.\n");

-        return AVERROR(EINVAL);

-    }

-    if (scale->w == -1 && scale->h == -1)

-        scale->w = scale->h = 0;

-

     return 0;

 }

@@ -118,6 +146,48 @@ static int config_props(AVFilterLink *outlink)

     AVFilterLink *inlink = outlink->src->inputs[0];

     ScaleContext *scale = ctx->priv;

     int64_t w, h;

+    double var_values[VARS_NB], res;

+    char *expr;

+    int ret;

+

+    var_values[VAR_PI]    = M_PI;

+    var_values[VAR_PHI]   = M_PHI;

+    var_values[VAR_E]     = M_E;

+    var_values[VAR_IN_W]  = var_values[VAR_IW] = inlink->w;

+    var_values[VAR_IN_H]  = var_values[VAR_IH] = inlink->h;

+    var_values[VAR_OUT_W] = var_values[VAR_OW] = NAN;

+    var_values[VAR_OUT_H] = var_values[VAR_OH] = NAN;

+    var_values[VAR_A]     = (float) inlink->w / inlink->h;

+    var_values[VAR_HSUB]  = 2<<av_pix_fmt_descriptors[inlink->format].log2_chroma_w;

+    var_values[VAR_VSUB]  = 2<<av_pix_fmt_descriptors[inlink->format].log2_chroma_h;

+

+    /* evaluate width and height */

+    av_expr_parse_and_eval(&res, (expr = scale->w_expr),

+                           var_names, var_values,

+                           NULL, NULL, NULL, NULL, NULL, 0, ctx);

+    scale->w = var_values[VAR_OW] = res;

+    if ((ret = av_expr_parse_and_eval(&res, (expr = scale->h_expr),

+                                      var_names, var_values,

+                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)

+        goto fail;

+    scale->h = var_values[VAR_OH] = res;

+    /* evaluate again the width, as it may depend on the output height */

+    if ((ret = av_expr_parse_and_eval(&res, (expr = scale->w_expr),

+                                      var_names, var_values,

+                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)

+        goto fail;

+    scale->w = res;

+

+    w = scale->w;

+    h = scale->h;

+

+    /* sanity check params */

+    if (w <  -1 || h <  -1) {

+        av_log(ctx, AV_LOG_ERROR, "Size values less than -1 are not acceptable.\n");

+        return AVERROR(EINVAL);

+    }

+    if (w == -1 && h == -1)

+        scale->w = scale->h = 0;

     if (!(w = scale->w))

         w = inlink->w;

@@ -159,6 +229,11 @@ static int config_props(AVFilterLink *outlink)

         return AVERROR(EINVAL);

     return 0;

+

+fail:

+    av_log(NULL, AV_LOG_ERROR,

+           "Error when evaluating the expression '%s'\n", expr);

+    return ret;

 }

 static void start_frame(AVFilterLink *link, AVFilterBufferRef *picref)