avfilter/formats: Add function to create AVFilterFormats with one entry

Most instances ff_add_formats() actually only ever add one format;
this function can be used to simplify those callers.
Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavfilter/formats.c

@@ -431,6 +431,12 @@ int ff_add_channel_layout(AVFilterChannelLayouts **l, uint64_t channel_layout)
     return 0;
 }
 
+AVFilterFormats *ff_make_formats_list_singleton(int fmt)
+{
+    int fmts[2] = { fmt, -1 };
+    return ff_make_format_list(fmts);
+}
+
 AVFilterFormats *ff_all_formats(enum AVMediaType type)
 {
     AVFilterFormats *ret = NULL;

libavfilter/formats.h

@@ -208,6 +208,12 @@ int ff_default_query_formats(AVFilterContext *ctx);
 av_warn_unused_result
 AVFilterFormats *ff_make_format_list(const int *fmts);
 
+/**
+ * Equivalent to ff_make_format_list({const int[]}{ fmt, -1 })
+ */
+av_warn_unused_result
+AVFilterFormats *ff_make_formats_list_singleton(int fmt);
+
 /**
  * Add fmt to the list of media formats contained in *avff.
  * If *avff is NULL the function allocates the filter formats struct