[FFmpeg-devel] [PATCH] lavu: add AVVideoHint API

[Anton Khirnov <anton@khirnov.net>]

From: Elias Carotti <eliascrt _at_ amazon _dot_ it>

Add side data type to provide hint to the video encoders about unchanged
portions of each frame.

Signed-off-by: Anton Khirnov <anton@khirnov.net>
---
I've made couple small changes:
* rebased against current master
* consistently refer to rectangles or AVVideoRect, not blocks
* use size_t instead of int for AVVideoHint.nb_rects
* build unconditionally -- this is public API, it must always be
  available regardless of what encoders are or are not available
* tweaked documentation

If you have no objections to the changes, I'll push this in a few days.
---
 doc/APIchanges         |   3 ++
 libavutil/Makefile     |   2 +
 libavutil/frame.h      |  10 ++++
 libavutil/version.h    |   2 +-
 libavutil/video_hint.c |  82 +++++++++++++++++++++++++++++++
 libavutil/video_hint.h | 108 +++++++++++++++++++++++++++++++++++++++++
 6 files changed, 206 insertions(+), 1 deletion(-)
 create mode 100644 libavutil/video_hint.c
 create mode 100644 libavutil/video_hint.h

diff --git a/doc/APIchanges b/doc/APIchanges
index 27f835cfce..0cda51fdee 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2023-02-09
 
 API changes, most recent first:
 
+2023-07-xx - xxxxxxxxxx - lavu 58.15.100 - video_hint.h
+  Add AVVideoHint API.
+
 2023-07-05 - xxxxxxxxxx - lavu 58.14.100 - random_seed.h
   Add av_random_bytes()
 
diff --git a/libavutil/Makefile b/libavutil/Makefile
index bd9c6f9e32..7828c94dc5 100644
--- a/libavutil/Makefile
+++ b/libavutil/Makefile
@@ -91,6 +91,7 @@ HEADERS = adler32.h                                                     \
           tea.h                                                         \
           tx.h                                                          \
           film_grain_params.h                                           \
+          video_hint.h
 
 ARCH_HEADERS = bswap.h                                                  \
                intmath.h                                                \
@@ -181,6 +182,7 @@ OBJS = adler32.o                                                        \
        uuid.o                                                           \
        version.o                                                        \
        video_enc_params.o                                               \
+       video_hint.o                                                     \
        film_grain_params.o                                              \
 
 
diff --git a/libavutil/frame.h b/libavutil/frame.h
index a491315f25..c0c1b23db7 100644
--- a/libavutil/frame.h
+++ b/libavutil/frame.h
@@ -214,6 +214,16 @@ enum AVFrameSideDataType {
      * Ambient viewing environment metadata, as defined by H.274.
      */
     AV_FRAME_DATA_AMBIENT_VIEWING_ENVIRONMENT,
+
+    /**
+     * Provide encoder-specific hinting information about changed/unchanged
+     * portions of a frame.  It can be used to pass information about which
+     * macroblocks can be skipped because they didn't change from the
+     * corresponding ones in the previous frame. This could be useful for
+     * applications which know this information in advance to speed up
+     * encoding.
+     */
+    AV_FRAME_DATA_VIDEO_HINT,
 };
 
 enum AVActiveFormatDescription {
diff --git a/libavutil/version.h b/libavutil/version.h
index 24af520e08..9e798b0e3f 100644
--- a/libavutil/version.h
+++ b/libavutil/version.h
@@ -79,7 +79,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  58
-#define LIBAVUTIL_VERSION_MINOR  14
+#define LIBAVUTIL_VERSION_MINOR  15
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
diff --git a/libavutil/video_hint.c b/libavutil/video_hint.c
new file mode 100644
index 0000000000..5730ed6cfb
--- /dev/null
+++ b/libavutil/video_hint.c
@@ -0,0 +1,82 @@
+/*
+ * Copyright 2023 Elias Carotti <eliascrt at amazon dot it>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <string.h>
+
+#include "avstring.h"
+#include "frame.h"
+#include "macros.h"
+#include "mem.h"
+#include "video_hint.h"
+
+AVVideoHint *av_video_hint_alloc(size_t nb_rects,
+                                 size_t *out_size)
+{
+    struct TestStruct {
+        AVVideoHint    hint;
+        AVVideoRect    rect;
+    };
+    const size_t rect_offset = offsetof(struct TestStruct, rect);
+    size_t size = rect_offset;
+    AVVideoHint *hint;
+
+    *out_size = 0;
+    if (nb_rects > (SIZE_MAX - size) / sizeof(AVVideoRect))
+        return NULL;
+    size += sizeof(AVVideoRect) * nb_rects;
+
+    hint = av_mallocz(size);
+    if (!hint)
+        return NULL;
+
+    hint->nb_rects    = nb_rects;
+    hint->rect_offset = rect_offset;
+    hint->rect_size   = sizeof(AVVideoRect);
+
+    *out_size = size;
+
+    return hint;
+}
+
+AVVideoHint *av_video_hint_create_side_data(AVFrame *frame,
+                                            size_t nb_rects)
+{
+    AVVideoHint *hint;
+    AVBufferRef *buf;
+    size_t size = 0;
+
+    hint = av_video_hint_alloc(nb_rects, &size);
+    if (!hint)
+        return NULL;
+
+    buf = av_buffer_create((uint8_t *)hint, size, NULL, NULL, 0);
+    if (!buf) {
+        av_freep(&hint);
+        return NULL;
+    }
+
+    if (!av_frame_new_side_data_from_buf(frame, AV_FRAME_DATA_VIDEO_HINT, buf)) {
+        av_buffer_unref(&buf);
+        return NULL;
+    }
+
+    return hint;
+}
+
diff --git a/libavutil/video_hint.h b/libavutil/video_hint.h
new file mode 100644
index 0000000000..86addf5ceb
--- /dev/null
+++ b/libavutil/video_hint.h
@@ -0,0 +1,108 @@
+/**
+ * Copyright 2023 Elias Carotti <eliascrt at amazon dot it>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVUTIL_VIDEO_HINT_H
+#define AVUTIL_VIDEO_HINT_H
+
+#include <stddef.h>
+#include <stdint.h>
+#include "libavutil/avassert.h"
+#include "libavutil/frame.h"
+
+typedef struct AVVideoRect {
+    uint32_t x, y;
+    uint32_t width, height;
+} AVVideoRect;
+
+typedef enum AVVideoHintType {
+    /* rectangled delimit the constant areas (unchanged), default is changed */
+    AV_VIDEO_HINT_CONSTANT,
+
+    /* rectangled delimit the constant areas (changed), default is not changed */
+    AV_VIDEO_HINT_CHANGED,
+} AVVideoHintType;
+
+typedef struct AVVideoHint {
+    /**
+     * Number of AVVideoRect present.
+     *
+     * May be 0, in which case no per-rectangle information is present. In this
+     * case the values of rect_offset / rect_size are unspecified and should
+     * not be accessed.
+     */
+    size_t nb_rects;
+
+    /**
+     * Offset in bytes from the beginning of this structure at which the array
+     * of AVVideoRect starts.
+     */
+    size_t rect_offset;
+
+    /**
+     * Size in bytes of AVVideoRect.
+     */
+    size_t rect_size;
+
+    AVVideoHintType type;
+} AVVideoHint;
+
+static av_always_inline AVVideoRect*
+av_video_hint_rects(const AVVideoHint *hints)
+{
+    return (AVVideoRect *)((uint8_t *)hints + hints->rect_offset);
+}
+
+static av_always_inline AVVideoRect*
+av_video_hint_get_rect(const AVVideoHint *hints, size_t idx)
+{
+    return (AVVideoRect *)((uint8_t *)hints + hints->rect_offset + idx * hints->rect_size);
+}
+
+/**
+ * Allocate memory for the AVVideoHint struct along with an nb_rects-sized
+ * arrays of AVVideoRect.
+ *
+ * The side data contains a list of rectangles for the portions of the frame
+ * which changed from the last encoded one (and the remainder are assumed to be
+ * changed), or, alternately (depending on the type parameter) the unchanged
+ * ones (and the remanining ones are those which changed).
+ * Macroblocks will thus be hinted either to be P_SKIP-ped or go through the
+ * regular encoding procedure.
+ *
+ * It's responsibility of the caller to fill the AVRects accordingly, and to set
+ * the proper AVVideoHintType field.
+ *
+ * @param out_size if non-NULL, the size in bytes of the resulting data array is
+ *                 written here
+ *
+ * @return newly allocated AVVideoHint struct (must be freed by the caller using
+ *         av_free()) on success, NULL on memory allocation failure
+ */
+AVVideoHint *av_video_hint_alloc(size_t nb_rects,
+                                 size_t *out_size);
+/**
+ * Same as av_video_hint_alloc(), except newly-allocated AVVideoHint is attached
+ * as side data of type AV_FRAME_DATA_VIDEO_HINT_INFO to frame.
+ */
+AVVideoHint *av_video_hint_create_side_data(AVFrame *frame,
+                                            size_t nb_rects);
+
+
+#endif /* AVUTIL_VIDEO_HINT_H */
-- 
2.40.1

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