lavu: add side data AV_FRAME_DATA_DETECTION_BBOXES for object detection/classification

doc/APIchanges

@@ -14,6 +14,8 @@ libavutil:     2017-10-21
 
 
 API changes, most recent first:
+2021-04-17 - xxxxxxxxxx - lavu 56.73.100 - frame.h detection_bbox.h
+  Add AV_FRAME_DATA_DETECTION_BBOXES
 
 2021-04-06 - xxxxxxxxxx - lavf 58.78.100 - avformat.h
   Add avformat_index_get_entries_count(), avformat_index_get_entry(),

libavutil/Makefile

@@ -21,6 +21,7 @@ HEADERS = adler32.h                                                     \
           cpu.h                                                         \
           crc.h                                                         \
           des.h                                                         \
+          detection_bbox.h                                              \
           dict.h                                                        \
           display.h                                                     \
           dovi_meta.h                                                   \
@@ -113,6 +114,7 @@ OBJS = adler32.o                                                        \
        cpu.o                                                            \
        crc.o                                                            \
        des.o                                                            \
+       detection_bbox.o                                                 \
        dict.o                                                           \
        display.o                                                        \
        dovi_meta.o                                                      \

libavutil/detection_bbox.c

@@ -0,0 +1,73 @@
+/*
+ * 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 "detection_bbox.h"
+
+AVDetectionBBoxHeader *av_detection_bbox_alloc(uint32_t nb_bboxes, size_t *out_size)
+{
+    size_t size;
+    struct {
+        AVDetectionBBoxHeader header;
+        AVDetectionBBox boxes[1];
+    } *ret;
+
+    size = sizeof(*ret);
+    if (nb_bboxes - 1 > (SIZE_MAX - size) / sizeof(*ret->boxes))
+        return NULL;
+    size += sizeof(*ret->boxes) * (nb_bboxes - 1);
+
+    ret = av_mallocz(size);
+    if (!ret)
+        return NULL;
+
+    ret->header.nb_bboxes = nb_bboxes;
+    ret->header.bbox_size = sizeof(*ret->boxes);
+    ret->header.bboxes_offset = (char *)&ret->boxes - (char *)&ret->header;
+
+    if (out_size)
+        *out_size = size;
+
+    return &ret->header;
+}
+
+AVDetectionBBoxHeader *av_detection_bbox_create_side_data(AVFrame *frame, uint32_t nb_bboxes)
+{
+    AVBufferRef         *buf;
+    AVDetectionBBoxHeader *header;
+    size_t size;
+
+    header = av_detection_bbox_alloc(nb_bboxes, &size);
+    if (!header)
+        return NULL;
+    if (size > INT_MAX) {
+        av_freep(&header);
+        return NULL;
+    }
+    buf = av_buffer_create((uint8_t *)header, size, NULL, NULL, 0);
+    if (!buf) {
+        av_freep(&header);
+        return NULL;
+    }
+
+    if (!av_frame_new_side_data_from_buf(frame, AV_FRAME_DATA_DETECTION_BBOXES, buf)) {
+        av_buffer_unref(&buf);
+        return NULL;
+    }
+
+    return header;
+}

libavutil/detection_bbox.h

@@ -0,0 +1,107 @@
+/*
+ * 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_DETECTION_BBOX_H
+#define AVUTIL_DETECTION_BBOX_H
+
+#include "rational.h"
+#include "avassert.h"
+#include "frame.h"
+
+typedef struct AVDetectionBBox {
+    /**
+     * Distance in pixels from the left/top edge of the frame,
+     * together with width and height, defining the bounding box.
+     */
+    int x;
+    int y;
+    int w;
+    int h;
+
+#define AV_DETECTION_BBOX_LABEL_NAME_MAX_SIZE 64
+
+    /**
+     * Detect result with confidence
+     */
+    char detect_label[AV_DETECTION_BBOX_LABEL_NAME_MAX_SIZE];
+    AVRational detect_confidence;
+
+    /**
+     * At most 4 classifications based on the detected bounding box.
+     * For example, we can get max 4 different attributes with 4 different
+     * DNN models on one bounding box.
+     * classify_count is zero if no classification.
+     */
+#define AV_NUM_BBOX_CLASSIFY 4
+    uint32_t classify_count;
+    char classify_labels[AV_NUM_BBOX_CLASSIFY][AV_DETECTION_BBOX_LABEL_NAME_MAX_SIZE];
+    AVRational classify_confidences[AV_NUM_BBOX_CLASSIFY];
+} AVDetectionBBox;
+
+typedef struct AVDetectionBBoxHeader {
+    /**
+     * Information about how the bounding box is generated.
+     * for example, the DNN model name.
+     */
+    char source[256];
+
+    /**
+     * Number of bounding boxes in the array.
+     */
+    uint32_t nb_bboxes;
+
+    /**
+     * Offset in bytes from the beginning of this structure at which
+     * the array of bounding boxes starts.
+     */
+    size_t bboxes_offset;
+
+    /**
+     * Size of each bounding box in bytes.
+     */
+    size_t bbox_size;
+} AVDetectionBBoxHeader;
+
+/*
+ * Get the bounding box at the specified {@code idx}. Must be between 0 and nb_bboxes.
+ */
+static av_always_inline AVDetectionBBox*
+av_get_detection_bbox(const AVDetectionBBoxHeader *header, unsigned int idx)
+{
+    av_assert0(idx < header->nb_bboxes);
+    return (AVDetectionBBox *)((uint8_t *)header + header->bboxes_offset +
+                               idx * header->bbox_size);
+}
+
+/**
+ * Allocates memory for AVDetectionBBoxHeader, plus an array of {@code nb_bboxes}
+ * AVDetectionBBox, and initializes the variables.
+ * Can be freed with a normal av_free() call.
+ *
+ * @param out_size if non-NULL, the size in bytes of the resulting data array is
+ * written here.
+ */
+AVDetectionBBoxHeader *av_detection_bbox_alloc(uint32_t nb_bboxes, size_t *out_size);
+
+/**
+ * Allocates memory for AVDetectionBBoxHeader, plus an array of {@code nb_bboxes}
+ * AVDetectionBBox, in the given AVFrame {@code frame} as AVFrameSideData of type
+ * AV_FRAME_DATA_DETECTION_BBOXES and initializes the variables.
+ */
+AVDetectionBBoxHeader *av_detection_bbox_create_side_data(AVFrame *frame, uint32_t nb_bboxes);
+#endif

libavutil/frame.c

@@ -853,6 +853,7 @@ const char *av_frame_side_data_name(enum AVFrameSideDataType type)
     case AV_FRAME_DATA_VIDEO_ENC_PARAMS:            return "Video encoding parameters";
     case AV_FRAME_DATA_SEI_UNREGISTERED:            return "H.26[45] User Data Unregistered SEI message";
     case AV_FRAME_DATA_FILM_GRAIN_PARAMS:           return "Film grain parameters";
+    case AV_FRAME_DATA_DETECTION_BBOXES:            return "Bounding boxes for object detection and classification";
     }
     return NULL;
 }

libavutil/frame.h

@@ -198,6 +198,12 @@ enum AVFrameSideDataType {
      * Must be present for every frame which should have film grain applied.
      */
     AV_FRAME_DATA_FILM_GRAIN_PARAMS,
+
+    /**
+     * Bounding boxes for object detection and classification,
+     * as described by AVDetectionBBoxHeader.
+     */
+    AV_FRAME_DATA_DETECTION_BBOXES,
 };
 
 enum AVActiveFormatDescription {

libavutil/version.h

@@ -79,7 +79,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  56
-#define LIBAVUTIL_VERSION_MINOR  72
+#define LIBAVUTIL_VERSION_MINOR  73
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \