diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index 076f2fd953..844e971d42 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -68,7 +68,7 @@ OBJS-$(CONFIG_CABAC)                   += cabac.o
 OBJS-$(CONFIG_CBS)                     += cbs.o
 OBJS-$(CONFIG_CBS_AV1)                 += cbs_av1.o
 OBJS-$(CONFIG_CBS_H264)                += cbs_h2645.o cbs_h264.o h2645_parse.o
-OBJS-$(CONFIG_CBS_H265)                += cbs_h2645.o h2645_parse.o
+OBJS-$(CONFIG_CBS_H265)                += cbs_h2645.o cbs_h265.o h2645_parse.o
 OBJS-$(CONFIG_CBS_JPEG)                += cbs_jpeg.o
 OBJS-$(CONFIG_CBS_MPEG2)               += cbs_mpeg2.o
 OBJS-$(CONFIG_CBS_VP9)                 += cbs_vp9.o
diff --git a/libavcodec/cbs_h265.c b/libavcodec/cbs_h265.c
new file mode 100644
index 0000000000..afbdd37896
--- /dev/null
+++ b/libavcodec/cbs_h265.c
@@ -0,0 +1,100 @@
+/*
+ * 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 "libavutil/mathematics.h"
+#include "libavutil/mastering_display_metadata.h"
+
+#include "cbs_h265.h"
+
+
+static uint32_t rescale_clip(AVRational value, uint32_t scale, uint32_t max)
+{
+    int64_t scaled = av_rescale(scale, value.num, value.den);
+    return av_clip64(scaled, 0, max);
+}
+
+static uint32_t rescale_fraction(AVRational value, uint32_t max)
+{
+    return rescale_clip(value, max, max);
+}
+
+void ff_cbs_h265_fill_sei_mastering_display(H265RawSEIMasteringDisplayColourVolume *mdcv,
+                                            const AVMasteringDisplayMetadata *mdm)
+{
+    memset(mdcv, 0, sizeof(*mdcv));
+
+    if (mdm->has_primaries) {
+        // The values in the metadata structure are fractions between 0 and 1,
+        // while the SEI message contains fixed-point values with an increment
+        // of 0.00002.  So, scale up by 50000 to convert between them.
+
+        for (int a = 0; a < 3; a++) {
+            // The metadata structure stores this in RGB order, but the SEI
+            // wants it in GBR order.
+            static const uint8_t mapping[] = { 1, 2, 0 };
+            int b = mapping[a];
+            mdcv->display_primaries_x[a] =
+                rescale_fraction(mdm->display_primaries[b][0], 50000);
+            mdcv->display_primaries_y[a] =
+                rescale_fraction(mdm->display_primaries[b][1], 50000);
+        }
+
+        mdcv->white_point_x = rescale_fraction(mdm->white_point[0], 50000);
+        mdcv->white_point_y = rescale_fraction(mdm->white_point[1], 50000);
+    }
+
+    if (mdm->has_luminance) {
+        // Metadata are rational values in candelas per square metre, SEI
+        // contains fixed point in units of 0.0001 candelas per square
+        // metre.  So scale up by 10000 to convert between them, and clip to
+        // ensure that we don't overflow.
+
+        mdcv->max_display_mastering_luminance =
+            rescale_clip(mdm->max_luminance, 10000, UINT32_MAX);
+        mdcv->min_display_mastering_luminance =
+            rescale_clip(mdm->min_luminance, 10000, UINT32_MAX);
+
+        // The spec has a hard requirement that min is less than the max,
+        // and the SEI-writing code enforces that.
+        if (!(mdcv->min_display_mastering_luminance <
+              mdcv->max_display_mastering_luminance)) {
+            if (mdcv->max_display_mastering_luminance == UINT32_MAX)
+                mdcv->min_display_mastering_luminance =
+                    mdcv->max_display_mastering_luminance - 1;
+            else
+                mdcv->max_display_mastering_luminance =
+                    mdcv->min_display_mastering_luminance + 1;
+        }
+    } else {
+        mdcv->max_display_mastering_luminance = 1;
+        mdcv->min_display_mastering_luminance = 0;
+    }
+}
+
+void ff_cbs_h265_fill_sei_content_light_level(H265RawSEIContentLightLevelInfo *cll,
+                                              const AVContentLightMetadata *clm)
+{
+    memset(cll, 0, sizeof(*cll));
+
+    // Both the metadata and the SEI are in units of candelas per square
+    // metre, so we only need to clip to ensure that they are in the valid
+    // range.
+
+    cll->max_content_light_level     = av_clip_uintp2(clm->MaxCLL,  16);
+    cll->max_pic_average_light_level = av_clip_uintp2(clm->MaxFALL, 16);
+}
diff --git a/libavcodec/cbs_h265.h b/libavcodec/cbs_h265.h
index f5eb5af5b2..793675ad41 100644
--- a/libavcodec/cbs_h265.h
+++ b/libavcodec/cbs_h265.h
@@ -746,4 +746,22 @@ typedef struct CodedBitstreamH265Context {
 } CodedBitstreamH265Context;
 
 
+struct AVMasteringDisplayMetadata;
+struct AVContentLightMetadata;
+
+/**
+ * Fill an SEI Mastering Display Colour Volume structure with values derived
+ * from the AVMasteringDisplayMetadata side-data structure.
+ */
+void ff_cbs_h265_fill_sei_mastering_display(H265RawSEIMasteringDisplayColourVolume *mdcv,
+                                            const struct AVMasteringDisplayMetadata *mdm);
+
+/**
+ * Fill an SEI Content Light Level Info structure with values derived from
+ * the AVContentLightMetadata side-data structure.
+ */
+void ff_cbs_h265_fill_sei_content_light_level(H265RawSEIContentLightLevelInfo *cll,
+                                              const struct AVContentLightMetadata *clm);
+
+
 #endif /* AVCODEC_CBS_H265_H */
