[FFmpeg-devel,v6,2/2] avutil: add HDR10+ dynamic metadata serialization function

diff --git a/doc/APIchanges b/doc/APIchanges
index 14737223cb..3a61d61931 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -2,6 +2,11 @@  The last version increases of all libraries were on 2023-02-09
 
 API changes, most recent first:
 
+2023-03-13 - xxxxxxxxxx - lavu 58.4.100 - hdr_dynamic_metadata.h
+  Add av_dynamic_hdr_plus_from_t35() and av_dynamic_hdr_plus_to_t35()
+  functions to convert between raw T.35 payloads containing dynamic
+  HDR10+ metadata and their parsed representations as AVDynamicHDRPlus.
+
 2023-03-02 - xxxxxxxxxx - lavc 60.6.100 - avcodec.h
   Add FF_PROFILE_EAC3_DDP_ATMOS, FF_PROFILE_TRUEHD_ATMOS,
   FF_PROFILE_DTS_HD_MA_X and FF_PROFILE_DTS_HD_MA_X_IMAX.
diff --git a/libavutil/hdr_dynamic_metadata.c b/libavutil/hdr_dynamic_metadata.c
index 223db2fd66..da3c5f4947 100644
--- a/libavutil/hdr_dynamic_metadata.c
+++ b/libavutil/hdr_dynamic_metadata.c
@@ -20,6 +20,7 @@ 
 
 #include "hdr_dynamic_metadata.h"
 #include "mem.h"
+#include "libavcodec/defs.h"
 #include "libavcodec/get_bits.h"
 #include "libavcodec/put_bits.h"
 
@@ -225,3 +226,150 @@  int av_dynamic_hdr_plus_from_t35(AVDynamicHDRPlus *s, const uint8_t *data,
 
     return 0;
 }
+
+int av_dynamic_hdr_plus_to_t35(const AVDynamicHDRPlus *s, uint8_t **data, size_t *size)
+{
+    uint8_t *buf;
+    size_t size_bits, size_bytes;
+    PutBitContext pbc, *pb = &pbc;
+
+    if (!s || !data)
+        return AVERROR(EINVAL);
+
+    /**
+     * Buffer size per CTA-861-H p.253-254:
+     * 48 bits for the header (56 minus excluded 8-bit country code)
+     * 2 bits for num_windows
+     * 937 bits for window geometry, for each window above 1
+     * 27 bits for targeted_system_display_maximum_luminance
+     * 1-3855 bits for targeted system display peak luminance information
+     * 0-442 bits for intra-window pixel distribution information
+     * 1-3855 bits for mastering display peak luminance information
+     * 0-537 bits for per-window tonemapping information
+     * 0-21 bits for per-window color saturation mapping information
+     */
+    size_bits = 48 +
+        2 +
+        FFMAX((s->num_windows - 1), 0) * 937 +
+        27 +
+        1 + (s->targeted_system_display_actual_peak_luminance_flag ? 10 +
+            s->num_rows_targeted_system_display_actual_peak_luminance *
+            s->num_cols_targeted_system_display_actual_peak_luminance * 4 : 0) +
+        s->num_windows * 82;
+
+    for (int w = 0; w < s->num_windows; w++)
+        size_bits += s->params[w].num_distribution_maxrgb_percentiles * 24;
+
+    size_bits += 1 + (s->mastering_display_actual_peak_luminance_flag ? 10 +
+        s->num_rows_mastering_display_actual_peak_luminance *
+        s->num_cols_mastering_display_actual_peak_luminance * 4 : 0) +
+        s->num_windows * 1;
+
+    for (int w = 0; w < s->num_windows; w++) {
+        if (s->params[w].tone_mapping_flag)
+            size_bits += 28 + s->params[w].num_bezier_curve_anchors * 10;
+    }
+
+    size_bits += s->num_windows * 1;
+    for (int w = 0; w < s->num_windows; w++) {
+        if (s->params[w].color_saturation_mapping_flag)
+            size_bits += 6;
+    }
+
+    size_bytes = (size_bits + 7) / 8;
+
+    // Pad the allocated buffer to account for optimized readers that may use it directly.
+    buf = av_malloc(size_bytes + AV_INPUT_BUFFER_PADDING_SIZE);
+    if (!buf)
+        return AVERROR(ENOMEM);
+
+    init_put_bits(pb, buf, size_bytes);
+
+    // itu_t_t35_country_code shall be 0xB5 (USA) (excluded from the payload)
+    // itu_t_t35_terminal_provider_code shall be 0x003C
+    put_bits(pb, 16, 0x003C);
+    // itu_t_t35_terminal_provider_oriented_code is set to ST 2094-40
+    put_bits(pb, 16, 0x0001);
+    // application_identifier shall be set to 4
+    put_bits(pb, 8, 4);
+    // application_mode is set to Application Version 1
+    put_bits(pb, 8, 1);
+
+    // Payload as per CTA-861-H p.253-254
+    put_bits(pb, 2, s->num_windows);
+
+    for (int w = 1; w < s->num_windows; w++) {
+        put_bits(pb, 16, s->params[w].window_upper_left_corner_x.num / s->params[w].window_upper_left_corner_x.den);
+        put_bits(pb, 16, s->params[w].window_upper_left_corner_y.num / s->params[w].window_upper_left_corner_y.den);
+        put_bits(pb, 16, s->params[w].window_lower_right_corner_x.num / s->params[w].window_lower_right_corner_x.den);
+        put_bits(pb, 16, s->params[w].window_lower_right_corner_y.num / s->params[w].window_lower_right_corner_y.den);
+        put_bits(pb, 16, s->params[w].center_of_ellipse_x);
+        put_bits(pb, 16, s->params[w].center_of_ellipse_y);
+        put_bits(pb, 8, s->params[w].rotation_angle);
+        put_bits(pb, 16, s->params[w].semimajor_axis_internal_ellipse);
+        put_bits(pb, 16, s->params[w].semimajor_axis_external_ellipse);
+        put_bits(pb, 16, s->params[w].semiminor_axis_external_ellipse);
+        put_bits(pb, 1, s->params[w].overlap_process_option);
+    }
+
+    put_bits(pb, 27, s->targeted_system_display_maximum_luminance.num * luminance_den /
+        s->targeted_system_display_maximum_luminance.den);
+    put_bits(pb, 1, s->targeted_system_display_actual_peak_luminance_flag);
+    if (s->targeted_system_display_actual_peak_luminance_flag) {
+        put_bits(pb, 5, s->num_rows_targeted_system_display_actual_peak_luminance);
+        put_bits(pb, 5, s->num_cols_targeted_system_display_actual_peak_luminance);
+        for (int i = 0; i < s->num_rows_targeted_system_display_actual_peak_luminance; i++) {
+            for (int j = 0; j < s->num_cols_targeted_system_display_actual_peak_luminance; j++)
+                put_bits(pb, 4, s->targeted_system_display_actual_peak_luminance[i][j].num * peak_luminance_den /
+                    s->targeted_system_display_actual_peak_luminance[i][j].den);
+        }
+    }
+
+    for (int w = 0; w < s->num_windows; w++) {
+        for (int i = 0; i < 3; i++)
+            put_bits(pb, 17, s->params[w].maxscl[i].num * rgb_den / s->params[w].maxscl[i].den);
+        put_bits(pb, 17, s->params[w].average_maxrgb.num * rgb_den / s->params[w].average_maxrgb.den);
+        put_bits(pb, 4, s->params[w].num_distribution_maxrgb_percentiles);
+        for (int i = 0; i < s->params[w].num_distribution_maxrgb_percentiles; i++) {
+            put_bits(pb, 7, s->params[w].distribution_maxrgb[i].percentage);
+            put_bits(pb, 17, s->params[w].distribution_maxrgb[i].percentile.num * rgb_den /
+                s->params[w].distribution_maxrgb[i].percentile.den);
+        }
+        put_bits(pb, 10, s->params[w].fraction_bright_pixels.num * fraction_pixel_den /
+            s->params[w].fraction_bright_pixels.den);
+    }
+
+    put_bits(pb, 1, s->mastering_display_actual_peak_luminance_flag);
+    if (s->mastering_display_actual_peak_luminance_flag) {
+        put_bits(pb, 5, s->num_rows_mastering_display_actual_peak_luminance);
+        put_bits(pb, 5, s->num_cols_mastering_display_actual_peak_luminance);
+        for (int i = 0; i < s->num_rows_mastering_display_actual_peak_luminance; i++) {
+            for (int j = 0; j < s->num_cols_mastering_display_actual_peak_luminance; j++)
+                put_bits(pb, 4, s->mastering_display_actual_peak_luminance[i][j].num * peak_luminance_den /
+                    s->mastering_display_actual_peak_luminance[i][j].den);
+        }
+    }
+
+    for (int w = 0; w < s->num_windows; w++) {
+        put_bits(pb, 1, s->params[w].tone_mapping_flag);
+        if (s->params[w].tone_mapping_flag) {
+            put_bits(pb, 12, s->params[w].knee_point_x.num * knee_point_den / s->params[w].knee_point_x.den);
+            put_bits(pb, 12, s->params[w].knee_point_y.num * knee_point_den / s->params[w].knee_point_y.den);
+            put_bits(pb, 4, s->params[w].num_bezier_curve_anchors);
+            for (int i = 0; i < s->params[w].num_bezier_curve_anchors; i++)
+                put_bits(pb, 10, s->params[w].bezier_curve_anchors[i].num * bezier_anchor_den /
+                    s->params[w].bezier_curve_anchors[i].den);
+            put_bits(pb, 1, s->params[w].color_saturation_mapping_flag);
+            if (s->params[w].color_saturation_mapping_flag)
+                put_bits(pb, 6, s->params[w].color_saturation_weight.num * saturation_weight_den /
+                    s->params[w].color_saturation_weight.den);
+        }
+    }
+
+    flush_put_bits(pb);
+
+    *data = buf;
+    if (size)
+        *size = size_bytes;
+    return 0;
+}
diff --git a/libavutil/hdr_dynamic_metadata.h b/libavutil/hdr_dynamic_metadata.h
index 3d327241c1..52b4660f7d 100644
--- a/libavutil/hdr_dynamic_metadata.h
+++ b/libavutil/hdr_dynamic_metadata.h
@@ -21,6 +21,7 @@ 
 #ifndef AVUTIL_HDR_DYNAMIC_METADATA_H
 #define AVUTIL_HDR_DYNAMIC_METADATA_H
 
+#include "buffer.h"
 #include "frame.h"
 #include "rational.h"
 
@@ -351,4 +352,16 @@  AVDynamicHDRPlus *av_dynamic_hdr_plus_create_side_data(AVFrame *frame);
 int av_dynamic_hdr_plus_from_t35(AVDynamicHDRPlus *s, const uint8_t *data,
                                  size_t size);
 
+/**
+ * Serialize dynamic HDR10+ metadata to a user data registered ITU-T T.35 buffer,
+ * excluding the country code and beginning with the terminal provider code.
+ * @param s A pointer containing the decoded AVDynamicHDRPlus structure.
+ * @param data A pointer to a byte buffer to be allocated and filled
+ *             with the serialized metadata.
+ * @param size A pointer to a size to be set to the returned buffer's size (optional).
+ *
+ * @return 0 if succeed. Otherwise, returns the appropriate AVERROR.
+ */
+int av_dynamic_hdr_plus_to_t35(const AVDynamicHDRPlus *s, uint8_t **data, size_t *size);
+
 #endif /* AVUTIL_HDR_DYNAMIC_METADATA_H */
diff --git a/libavutil/version.h b/libavutil/version.h
index 900b798971..7635672985 100644
--- a/libavutil/version.h
+++ b/libavutil/version.h
@@ -79,7 +79,7 @@ 
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  58
-#define LIBAVUTIL_VERSION_MINOR   3
+#define LIBAVUTIL_VERSION_MINOR   4
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \