avfilter: Replace query_formats callback with union of list and callback

If one looks at the many query_formats callbacks in existence,
one will immediately recognize that there is one type of default
callback for video and a slightly different default callback for
audio: It is "return ff_set_common_formats_from_list(ctx, pix_fmts);"
for video with a filter-specific pix_fmts list. For audio, it is
the same with a filter-specific sample_fmts list together with
ff_set_common_all_samplerates() and ff_set_common_all_channel_counts().

This commit allows to remove the boilerplate query_formats callbacks
by replacing said callback with a union consisting the old callback
and pointers for pixel and sample format arrays. For the not uncommon
case in which these lists only contain a single entry (besides the
sentinel) enum AVPixelFormat and enum AVSampleFormat fields are also
added to the union to store them directly in the AVFilter,
thereby avoiding a relocation.

The state of said union will be contained in a new, dedicated AVFilter
field (the nb_inputs and nb_outputs fields have been shrunk to uint8_t
in order to create a hole for this new field; this is no problem, as
the maximum of all the nb_inputs is four; for nb_outputs it is only
two).

The state's default value coincides with the earlier default of
query_formats being unset, namely that the filter accepts all formats
(and also sample rates and channel counts/layouts for audio)
provided that these properties agree coincide for all inputs and
outputs.

By using different union members for audio and video filters
the type-unsafety of using the same functions for audio and video
lists will furthermore be more confined to formats.c than before.

When the new fields are used, they will also avoid allocations:
Currently something nearly equivalent to ff_default_query_formats()
is called after every successful call to a query_formats callback;
yet in the common case that the newly allocated AVFilterFormats
are not used at all (namely if there are no free links) these newly
allocated AVFilterFormats are freed again without ever being used.
Filters no longer using the callback will not exhibit this any more.

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

1 files changed, 46 insertions, 6 deletions

diff --git a/libavfilter/avfilter.h b/libavfilter/avfilter.h
index 69ecb0186d..566c1b87ce 100644
--- a/libavfilter/avfilter.h
+++ b/libavfilter/avfilter.h
@@ -203,12 +203,18 @@ typedef struct AVFilter {
     /**
      * The number of entries in the list of inputs.
      */
-    uint16_t nb_inputs;
+    uint8_t nb_inputs;
 
     /**
      * The number of entries in the list of outputs.
      */
-    uint16_t nb_outputs;
+    uint8_t nb_outputs;
+
+    /**
+     * This field determines the state of the formats union.
+     * It is an enum FilterFormatsState value.
+     */
+    uint8_t formats_state;
 
     /**
      * Filter pre-initialization function
@@ -274,6 +280,11 @@ typedef struct AVFilter {
     void (*uninit)(AVFilterContext *ctx);
 
     /**
+     * The state of the following union is determined by formats_state.
+     * See the documentation of enum FilterFormatsState in internal.h.
+     */
+    union {
+    /**
      * Query formats supported by the filter on its inputs and outputs.
      *
      * This callback is called after the filter is initialized (so the inputs
@@ -288,14 +299,43 @@ typedef struct AVFilter {
      * @ref AVFilterLink.incfg.channel_layouts "in_channel_layouts" /
      * @ref AVFilterLink.outcfg.channel_layouts "out_channel_layouts" analogously.
      *
-     * This callback may be NULL for filters with one input, in which case
-     * libavfilter assumes that it supports all input formats and preserves
-     * them on output.
+     * This callback must never be NULL if the union is in this state.
      *
      * @return zero on success, a negative value corresponding to an
      * AVERROR code otherwise
      */
-    int (*query_formats)(AVFilterContext *);
+        int (*query_func)(AVFilterContext *);
+        /**
+         * A pointer to an array of admissible pixel formats delimited
+         * by AV_PIX_FMT_NONE. The generic code will use this list
+         * to indicate that this filter supports each of these pixel formats,
+         * provided that all inputs and outputs use the same pixel format.
+         *
+         * This list must never be NULL if the union is in this state.
+         * The type of all inputs and outputs of filters using this must
+         * be AVMEDIA_TYPE_VIDEO.
+         */
+        const enum AVPixelFormat *pixels_list;
+        /**
+         * Analogous to pixels, but delimited by AV_SAMPLE_FMT_NONE
+         * and restricted to filters that only have AVMEDIA_TYPE_AUDIO
+         * inputs and outputs.
+         *
+         * In addition to that the generic code will mark all inputs
+         * and all outputs as supporting all sample rates and every
+         * channel count and channel layout, as long as all inputs
+         * and outputs use the same sample rate and channel count/layout.
+         */
+        const enum AVSampleFormat *samples_list;
+        /**
+         * Equivalent to { pix_fmt, AV_PIX_FMT_NONE } as pixels_list.
+         */
+        enum AVPixelFormat  pix_fmt;
+        /**
+         * Equivalent to { sample_fmt, AV_SAMPLE_FMT_NONE } as samples_list.
+         */
+        enum AVSampleFormat sample_fmt;
+    } formats;
 
     int priv_size;      ///< size of private data to allocate for the filter