lavu: add video_hint API

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>

libavutil/video_hint.c

@@ -0,0 +1,81 @@
+/*
+ * 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;
+}