lavfi/setpts: add FRAME_RATE constant

Useful for dealing with constant frame-rate video.

doc/filters.texi

@@ -4194,6 +4194,9 @@ Accept in input an expression evaluated through the eval API, which
 can contain the following constants:
 
 @table @option
+@item FRAME_RATE
+frame rate, only defined for constant frame-rate video
+
 @item PTS
 the presentation timestamp in input
 

libavfilter/f_setpts.c

@@ -35,6 +35,7 @@
 #include "video.h"
 
 static const char *const var_names[] = {
+    "FRAME_RATE",  ///< defined only for constant frame-rate video
     "INTERLACED",  ///< tell if the current frame is interlaced
     "N",           ///< frame number (starting at zero)
     "NB_CONSUMED_SAMPLES", ///< number of samples consumed by the filter (only audio)
@@ -54,6 +55,7 @@ static const char *const var_names[] = {
 };
 
 enum var_name {
+    VAR_FRAME_RATE,
     VAR_INTERLACED,
     VAR_N,
     VAR_NB_CONSUMED_SAMPLES,
@@ -107,8 +109,13 @@ static int config_input(AVFilterLink *inlink)
     if (setpts->type == AVMEDIA_TYPE_AUDIO)
         setpts->var_values[VAR_SAMPLE_RATE] = inlink->sample_rate;
 
-    av_log(inlink->src, AV_LOG_VERBOSE, "TB:%f SAMPLE_RATE:%f\n",
-           setpts->var_values[VAR_TB], setpts->var_values[VAR_SAMPLE_RATE]);
+    setpts->var_values[VAR_FRAME_RATE] = inlink->frame_rate.num && inlink->frame_rate.den ?
+        av_q2d(inlink->frame_rate) : NAN;
+
+    av_log(inlink->src, AV_LOG_VERBOSE, "TB:%f FRAME_RATE:%f SAMPLE_RATE:%f\n",
+           setpts->var_values[VAR_TB],
+           setpts->var_values[VAR_FRAME_RATE],
+           setpts->var_values[VAR_SAMPLE_RATE]);
     return 0;
 }
 

libavfilter/version.h

@@ -30,7 +30,7 @@
 
 #define LIBAVFILTER_VERSION_MAJOR  3
 #define LIBAVFILTER_VERSION_MINOR  16
-#define LIBAVFILTER_VERSION_MICRO 101
+#define LIBAVFILTER_VERSION_MICRO 102
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \