avfilter/avfilter: Deprecate avfilter_pad_count()

It is unnecessary as the number of static inputs and outputs can now
be directly read via AVFilter.nb_(in|out)puts.

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

doc/APIchanges

@@ -16,6 +16,7 @@ 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().
+  Deprecate avfilter_pad_count().
 
 2021-08-17 - xxxxxxxxxx - lavu 57.4.101 - opt.h
   av_opt_copy() now guarantees that allocated src and dst options

libavfilter/avfilter.c

@@ -538,6 +538,7 @@ int avfilter_process_command(AVFilterContext *filter, const char *cmd, const cha
     return AVERROR(ENOSYS);
 }
 
+#if FF_API_PAD_COUNT
 int avfilter_pad_count(const AVFilterPad *pads)
 {
     const AVFilter *filter;
@@ -555,6 +556,7 @@ int avfilter_pad_count(const AVFilterPad *pads)
 
     av_assert0(!"AVFilterPad list not from a filter");
 }
+#endif
 
 unsigned avfilter_filter_pad_count(const AVFilter *filter, int is_output)
 {

libavfilter/avfilter.h

@@ -70,10 +70,15 @@ typedef struct AVFilterPad     AVFilterPad;
 typedef struct AVFilterFormats AVFilterFormats;
 typedef struct AVFilterChannelLayouts AVFilterChannelLayouts;
 
+#if FF_API_PAD_COUNT
 /**
  * Get the number of elements in an AVFilter's inputs or outputs array.
+ *
+ * @deprecated Use avfilter_filter_pad_count() instead.
  */
+attribute_deprecated
 int avfilter_pad_count(const AVFilterPad *pads);
+#endif
 
 /**
  * Get the name of an AVFilterPad.

libavfilter/version.h

@@ -56,5 +56,8 @@
 #ifndef FF_API_BUFFERSINK_ALLOC
 #define FF_API_BUFFERSINK_ALLOC             (LIBAVFILTER_VERSION_MAJOR < 9)
 #endif
+#ifndef FF_API_PAD_COUNT
+#define FF_API_PAD_COUNT                    (LIBAVFILTER_VERSION_MAJOR < 9)
+#endif
 
 #endif /* AVFILTER_VERSION_H */