@@ -2075,6 +2075,16 @@ The following functions are available:

 @table @command

+@item expr, e

+The expression evaluation result.

+

+It must take one argument specifying the expression to be evaluated,

+which accepts the same constants and functions as the @var{x} and

+@var{y} values. Note that not all constants should be used, for

+example the text size is not known when evaluating the expression, so

+the constants @var{text_w} and @var{text_h} will have an undefined

+value.

+

 @item gmtime

 The time at which the filter is running, expressed in UTC.

 It can accept an argument: a strftime() format string.

@@ -30,7 +30,7 @@

 #define LIBAVFILTER_VERSION_MAJOR  3

 #define LIBAVFILTER_VERSION_MINOR  23

-#define LIBAVFILTER_VERSION_MICRO 103

+#define LIBAVFILTER_VERSION_MICRO 104

 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \

                                                LIBAVFILTER_VERSION_MINOR, \

@@ -643,12 +643,34 @@ static int func_strftime(AVFilterContext *ctx, AVBPrint *bp,

     return 0;

 }

+static int func_eval_expr(AVFilterContext *ctx, AVBPrint *bp,

+                          char *fct, unsigned argc, char **argv, int tag)

+{

+    DrawTextContext *dtext = ctx->priv;

+    double res;

+    int ret;

+

+    ret = av_expr_parse_and_eval(&res, argv[0], var_names, dtext->var_values,

+                                 NULL, NULL, fun2_names, fun2,

+                                 &dtext->prng, 0, ctx);

+    if (ret < 0)

+        av_log(ctx, AV_LOG_ERROR,

+               "Expression '%s' for the expr text expansion function is not valid\n",

+               argv[0]);

+    else

+        av_bprintf(bp, "%f", res);

+

+    return ret;

+}

+

 static const struct drawtext_function {

     const char *name;

     unsigned argc_min, argc_max;

     int tag; /** opaque argument to func */

     int (*func)(AVFilterContext *, AVBPrint *, char *, unsigned, char **, int);

 } functions[] = {

+    { "expr",      1, 1, 0,   func_eval_expr },

+    { "e",         1, 1, 0,   func_eval_expr },

     { "pts",       0, 0, 0,   func_pts      },

     { "gmtime",    0, 1, 'G', func_strftime },

     { "localtime", 0, 1, 'L', func_strftime },