avfilter: add ff_filter_get_nb_threads()

libavfilter/avfilter.c

@@ -783,6 +783,13 @@ void avfilter_free(AVFilterContext *filter)
     av_free(filter);
 }
 
+int ff_filter_get_nb_threads(AVFilterContext *ctx)
+{
+     if (ctx->nb_threads > 0)
+         return FFMIN(ctx->nb_threads, ctx->graph->nb_threads);
+     return ctx->graph->nb_threads;
+}
+
 static int process_options(AVFilterContext *ctx, AVDictionary **options,
                            const char *args)
 {

libavfilter/internal.h

@@ -402,4 +402,10 @@ static inline int ff_norm_qscale(int qscale, int type)
     return qscale;
 }
 
+/**
+ * Get number of threads for current filter instance.
+ * This number is always same or less than graph->nb_threads.
+ */
+int ff_filter_get_nb_threads(AVFilterContext *ctx);
+
 #endif /* AVFILTER_INTERNAL_H */