Re: [FFmpeg-devel] [PATCH] Optimization: support for libx264's mb_info

["Carotti, Elias" <eliascrt@amazon.it>]

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On Sat, 2023-07-01 at 10:33 +0200, Anton Khirnov wrote:
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> 
> 
> Sorry to still nag you, but I just noticed that unlike
> video_enc_params,
> you do not store AVVideoRect size in AVVideoHint. This means that
> no new fields can be added to AVVideoRect without an ABI break. This
> seems suboptimal, since I do see potential use for per-block
> information.
> 

Hi Anton,
I do agree with you. 
Please find the updated (and rebased) patch attached to this email.

Best,
Elias

P.S. By the way, I would be tempted  (I didn't do that here) to declare
the block_size field as 

const size_t block_size;

and then when setting it into av_video_hint_alloc(...) cast away the
const (it has to be assigned only once, upon allocation of the struct),
just to enforce compiler checking against accidental assignments and
for better clarity that this is a read-only field, in the general case.

P.P.S.: I'm sending the second part of the patch for libavcodec  as a
separate email. 


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> Anton Khirnov
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From b0fb79736c082d4c6c8bfd698f8f76a835d41770 Mon Sep 17 00:00:00 2001
From: Elias Carotti <eliascrt _at_ amazon _dot_ it>
Date: Tue, 20 Jun 2023 19:28:04 +0200
Subject: [PATCH 1/2] lavu: add AVVideoHint API

Add side data type to provide hint to the video encoders about unchanged
portions of each frame.
---
 doc/APIchanges         |  3 ++
 libavutil/Makefile     |  4 ++
 libavutil/frame.h      | 10 +++++
 libavutil/version.h    |  4 +-
 libavutil/video_hint.c | 82 ++++++++++++++++++++++++++++++++++++
 libavutil/video_hint.h | 94 ++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 195 insertions(+), 2 deletions(-)
 create mode 100644 libavutil/video_hint.c
 create mode 100644 libavutil/video_hint.h

diff --git a/doc/APIchanges b/doc/APIchanges
index f040211f7d..bfe04556d2 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:

+2023-06-21 - xxxxxxxxxx - lavu 58.14.100 - video_hint.h
+  Add AVVideoHint API.
+
 2023-05-29 - xxxxxxxxxx - lavc 60.16.100 - avcodec.h codec_id.h
   Add AV_CODEC_ID_EVC, FF_PROFILE_EVC_BASELINE, and FF_PROFILE_EVC_MAIN.

diff --git a/libavutil/Makefile b/libavutil/Makefile
index bd9c6f9e32..a0b43faa9f 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                                                \
@@ -188,6 +189,7 @@ OBJS-$(CONFIG_CUDA)                     += hwcontext_cuda.o
 OBJS-$(CONFIG_D3D11VA)                  += hwcontext_d3d11va.o
 OBJS-$(CONFIG_DXVA2)                    += hwcontext_dxva2.o
 OBJS-$(CONFIG_LIBDRM)                   += hwcontext_drm.o
+OBJS-$(CONFIG_LIBX264)                  += video_hint.o
 OBJS-$(CONFIG_MACOS_KPERF)              += macos_kperf.o
 OBJS-$(CONFIG_MEDIACODEC)               += hwcontext_mediacodec.o
 OBJS-$(CONFIG_OPENCL)                   += hwcontext_opencl.o
@@ -219,6 +221,8 @@ SKIPHEADERS-$(CONFIG_VULKAN)           += hwcontext_vulkan.h vulkan.h   \
                                           vulkan_functions.h            \
                                           vulkan_loader.h

+SKIPHEADERS-$(CONFIG_LIBX264)  	       += video_hint.h
+
 TESTPROGS = adler32                                                     \
             aes                                                         \
             aes_ctr                                                     \
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 17a6d296a6..24af520e08 100644
--- a/libavutil/version.h
+++ b/libavutil/version.h
@@ -79,8 +79,8 @@
  */

 #define LIBAVUTIL_VERSION_MAJOR  58
-#define LIBAVUTIL_VERSION_MINOR  13
-#define LIBAVUTIL_VERSION_MICRO 101
+#define LIBAVUTIL_VERSION_MINOR  14
+#define LIBAVUTIL_VERSION_MICRO 100

 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
                                                LIBAVUTIL_VERSION_MINOR, \
diff --git a/libavutil/video_hint.c b/libavutil/video_hint.c
new file mode 100644
index 0000000000..0ea495debe
--- /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 blocks_offset = offsetof(struct TestStruct, rect);
+    size_t size = blocks_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->blocks_offset = blocks_offset;
+    hint->block_size    = sizeof(AVVideoRect);
+
+    *out_size = size;
+
+    return hint;
+}
+
+AVVideoHint *av_video_hint_create_side_data(AVFrame *frame,
+                                            size_t num_rects)
+{
+    AVVideoHint *hint;
+    AVBufferRef *buf;
+    size_t size = 0;
+
+    hint = av_video_hint_alloc(num_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..469336e90d
--- /dev/null
+++ b/libavutil/video_hint.h
@@ -0,0 +1,94 @@
+/**
+ * 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 {
+    /* blocks delimit the constant areas (unchanged), default is changed */
+    AV_VIDEO_HINT_CONSTANT,
+
+    /* blocks delimit the constant areas (changed), default is not changed */
+    AV_VIDEO_HINT_CHANGED,
+} AVVideoHintType;
+
+typedef struct AVVideoHint {
+    /**
+     * Number of blocks in the array.
+     *
+     * May be 0, in which case no per-block information is present. In this case
+     * the values of blocks_offset / block_size are unspecified and should not
+     * be accessed.
+     */
+    int nb_rects;
+
+    /**
+     * Offset in bytes from the beginning of this structure at which the array
+     * of blocks starts.
+     */
+    size_t blocks_offset;
+
+    size_t block_size;
+
+    AVVideoHintType type;
+} AVVideoHint;
+
+static av_always_inline AVVideoRect*
+av_video_hint_rects(const AVVideoHint *hints)
+{
+    return (AVVideoRect *)((uint8_t *)hints + hints->blocks_offset);
+}
+
+static av_always_inline AVVideoRect*
+av_video_hint_get_rect(const AVVideoHint *hints, size_t idx)
+{
+    return (AVVideoRect *)((uint8_t *)hints + hints->blocks_offset + idx * hints->block_size);
+}
+
+/**
+ * Allocate memory for a vector of AVVideoRect in the given AVFrame
+ * {@code frame} as AVFrameSideData of type AV_FRAME_DATA_VIDEO_HINT_INFO.
+ * 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.
+ */
+AVVideoHint *av_video_hint_create_side_data(AVFrame *frame,
+                                            size_t num_rects);
+
+AVVideoHint *av_video_hint_alloc(size_t nb_rects,
+                                 size_t *out_size);
+
+#endif /* AVUTIL_VIDEO_HINT_H */
--
2.34.1


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