avfilter/af_ladspa: support simpler syntax for controls

Signed-off-by: Paul B Mahol <onemda@gmail.com>

doc/filters.texi

@@ -1970,6 +1970,9 @@ threshold or gain).
 Controls need to be defined using the following syntax:
 c0=@var{value0}|c1=@var{value1}|c2=@var{value2}|..., where
 @var{valuei} is the value set on the @var{i}-th control.
+Alternatively they can be also defined using the following syntax:
+@var{value0}|@var{value1}|@var{value2}|..., where
+@var{valuei} is the value set on the @var{i}-th control.
 If @option{controls} is set to @code{help}, all available controls and
 their valid ranges are printed.
 

libavfilter/af_ladspa.c

@@ -396,7 +396,7 @@ static av_cold int init(AVFilterContext *ctx)
     AVFilterPad pad = { NULL };
     char *p, *arg, *saveptr = NULL;
     unsigned long nb_ports;
-    int i;
+    int i, j = 0;
 
     if (!s->dl_name) {
         av_log(ctx, AV_LOG_ERROR, "No plugin name provided\n");
@@ -543,9 +543,12 @@ static av_cold int init(AVFilterContext *ctx)
         p = NULL;
 
         if (sscanf(arg, "c%d=%f", &i, &val) != 2) {
+            if (sscanf(arg, "%f", &val) != 1) {
                 av_log(ctx, AV_LOG_ERROR, "Invalid syntax.\n");
                 return AVERROR(EINVAL);
             }
+            i = j++;
+        }
 
         if ((ret = set_control(ctx, i, val)) < 0)
             return ret;