[FFmpeg-devel] [PATCH v2 1/2] avcodec/pngdec: read cLLi and mDVc chunks

[Leo Izen]

These chunks contain the Content Light Level Information and the
Mastering Display Color Volume information that FFmpeg already supports
as AVFrameSideData. This patch adds support for the png decoder to read
these chunks if present and attach the corresponding side data to the
decoded frame.

Signed-off-by: Leo Izen <leo.izen at gmail.com>
---
 libavcodec/pngdec.c | 63 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index d1aae4c70e..026da30c25 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -29,6 +29,7 @@
 #include "libavutil/csp.h"
 #include "libavutil/imgutils.h"
 #include "libavutil/intreadwrite.h"
+#include "libavutil/mastering_display_metadata.h"
 #include "libavutil/pixfmt.h"
 #include "libavutil/rational.h"
 #include "libavutil/stereo3d.h"
@@ -81,6 +82,14 @@ typedef struct PNGDecContext {
     enum AVColorPrimaries cicp_primaries;
     enum AVColorTransferCharacteristic cicp_trc;
     enum AVColorRange cicp_range;
+    int have_clli;
+    uint32_t clli_max;
+    uint32_t clli_avg;
+    int have_mdvc;
+    uint16_t mdvc_primaries[3][2];
+    uint16_t mdvc_white_point[2];
+    uint32_t mdvc_max_lum;
+    uint32_t mdvc_min_lum;
 
     enum PNGHeaderState hdr_state;
     enum PNGImageState pic_state;
@@ -731,6 +740,36 @@ static int populate_avctx_color_fields(AVCodecContext *avctx, AVFrame *frame)
     if (!s->has_trns && s->significant_bits > 0)
         avctx->bits_per_raw_sample = s->significant_bits;
 
+    if (s->have_clli) {
+        AVContentLightMetadata *clli =
+            av_content_light_metadata_create_side_data(frame);
+        if (!clli)
+            return AVERROR(ENOMEM);
+        /*
+         * 0.0001 divisor value
+         * see: https://www.w3.org/TR/png-3/#cLLi-chunk
+         */
+        clli->MaxCLL = s->clli_max / 10000;
+        clli->MaxFALL = s->clli_avg / 10000;
+    }
+
+    if (s->have_mdvc) {
+        AVMasteringDisplayMetadata *mdvc =
+            av_mastering_display_metadata_create_side_data(frame);
+        if (!mdvc)
+            return AVERROR(ENOMEM);
+        mdvc->has_primaries = 1;
+        for (int i = 0; i < 3; i++) {
+            mdvc->display_primaries[i][0] = av_make_q(s->mdvc_primaries[i][0], 50000);
+            mdvc->display_primaries[i][1] = av_make_q(s->mdvc_primaries[i][1], 50000);
+        }
+        mdvc->white_point[0] = av_make_q(s->mdvc_white_point[0], 50000);
+        mdvc->white_point[1] = av_make_q(s->mdvc_white_point[1], 50000);
+        mdvc->has_luminance = 1;
+        mdvc->max_luminance = av_make_q(s->mdvc_max_lum, 10000);
+        mdvc->min_luminance = av_make_q(s->mdvc_min_lum, 10000);
+    }
+
     return 0;
 }
 
@@ -1508,6 +1547,30 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
 
             break;
         }
+        case MKTAG('c', 'L', 'L', 'i'):
+            if (bytestream2_get_bytes_left(&gb_chunk) != 8) {
+                av_log(avctx, AV_LOG_WARNING, "Invalid cLLi chunk size: %d\n", bytestream2_get_bytes_left(&gb_chunk));
+                break;
+            }
+            s->have_clli = 1;
+            s->clli_max = bytestream2_get_be32u(&gb_chunk);
+            s->clli_avg = bytestream2_get_be32u(&gb_chunk);
+            break;
+        case MKTAG('m', 'D', 'V', 'c'):
+            if (bytestream2_get_bytes_left(&gb_chunk) != 24) {
+                av_log(avctx, AV_LOG_WARNING, "Invalid mDVc chunk size: %d\n", bytestream2_get_bytes_left(&gb_chunk));
+                break;
+            }
+            s->have_mdvc = 1;
+            for (int i = 0; i < 3; i++) {
+                s->mdvc_primaries[i][0] = bytestream2_get_be16u(&gb_chunk);
+                s->mdvc_primaries[i][1] = bytestream2_get_be16u(&gb_chunk);
+            }
+            s->mdvc_white_point[0] = bytestream2_get_be16u(&gb_chunk);
+            s->mdvc_white_point[1] = bytestream2_get_be16u(&gb_chunk);
+            s->mdvc_max_lum = bytestream2_get_be32u(&gb_chunk);
+            s->mdvc_min_lum = bytestream2_get_be32u(&gb_chunk);
+            break;
         case MKTAG('I', 'E', 'N', 'D'):
             if (!(s->pic_state & PNG_ALLIMAGE))
                 av_log(avctx, AV_LOG_ERROR, "IEND without all image\n");
-- 
2.43.0