avfilter/avfilter: Add avfilter_filter_pad_count()

It is intended as replacement for avfilter_pad_count(). In contrast to
the latter, it avoids a loop.

Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

doc/APIchanges

@@ -14,6 +14,9 @@ libavutil:     2021-04-27
 
 API changes, most recent first:
 
+2021-08-20 - xxxxxxxxxx - lavfi 8.3.100 - avfilter.H
+  Add avfilter_filter_pad_count() as a replacement for avfilter_pad_count().
+
 2021-08-17 - xxxxxxxxxx - lavu 57.4.101 - opt.h
   av_opt_copy() now guarantees that allocated src and dst options
   don't alias each other even on error.

libavfilter/avfilter.c

@@ -556,6 +556,11 @@ int avfilter_pad_count(const AVFilterPad *pads)
     av_assert0(!"AVFilterPad list not from a filter");
 }
 
+unsigned avfilter_filter_pad_count(const AVFilter *filter, int is_output)
+{
+    return is_output ? filter->nb_outputs : filter->nb_inputs;
+}
+
 static const char *default_filter_name(void *filter_ctx)
 {
     AVFilterContext *ctx = filter_ctx;

libavfilter/avfilter.h

@@ -325,6 +325,11 @@ typedef struct AVFilter {
     int (*activate)(AVFilterContext *ctx);
 } AVFilter;
 
+/**
+ * Get the number of elements in an AVFilter's inputs or outputs array.
+ */
+unsigned avfilter_filter_pad_count(const AVFilter *filter, int is_output);
+
 /**
  * Process multiple parts of the frame concurrently.
  */

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   8
-#define LIBAVFILTER_VERSION_MINOR   2
+#define LIBAVFILTER_VERSION_MINOR   3
 #define LIBAVFILTER_VERSION_MICRO 100