[FFmpeg-devel] [PATCH v2 2/2] avcodec/pngenc: write 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 encoder to save
this metadata as the corresponding chunks in the PNG stream.

Signed-off-by: Leo Izen <leo.izen at gmail.com>
---
 libavcodec/pngenc.c | 32 +++++++++++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/libavcodec/pngenc.c b/libavcodec/pngenc.c
index f0650962d2..50689cb50c 100644
--- a/libavcodec/pngenc.c
+++ b/libavcodec/pngenc.c
@@ -32,6 +32,7 @@
 #include "libavutil/crc.h"
 #include "libavutil/csp.h"
 #include "libavutil/libm.h"
+#include "libavutil/mastering_display_metadata.h"
 #include "libavutil/opt.h"
 #include "libavutil/rational.h"
 #include "libavutil/stereo3d.h"
@@ -294,8 +295,9 @@ static int png_write_row(AVCodecContext *avctx, const uint8_t *data, int size)
     return 0;
 }
 
-#define AV_WB32_PNG(buf, n) AV_WB32(buf, lrint((n) * 100000))
-#define AV_WB32_PNG_D(buf, d) AV_WB32_PNG(buf, av_q2d(d))
+#define PNG_LRINT(d, divisor) lrint((d) * (divisor))
+#define PNG_Q2D(q, divisor) PNG_LRINT(av_q2d(q), (divisor))
+#define AV_WB32_PNG_D(buf, q) AV_WB32(buf, PNG_Q2D(q, 100000))
 static int png_get_chrm(enum AVColorPrimaries prim,  uint8_t *buf)
 {
     const AVColorPrimariesDesc *desc = av_csp_primaries_desc_from_id(prim);
@@ -320,7 +322,7 @@ static int png_get_gama(enum AVColorTransferCharacteristic trc, uint8_t *buf)
     if (gamma <= 1e-6)
         return 0;
 
-    AV_WB32_PNG(buf, 1.0 / gamma);
+    AV_WB32(buf, PNG_LRINT(1.0 / gamma, 100000));
     return 1;
 }
 
@@ -437,6 +439,30 @@ static int encode_headers(AVCodecContext *avctx, const AVFrame *pict)
         png_write_chunk(&s->bytestream, MKTAG('c', 'I', 'C', 'P'), s->buf, 4);
     }
 
+    side_data = av_frame_get_side_data(pict, AV_FRAME_DATA_CONTENT_LIGHT_LEVEL);
+    if (side_data) {
+        AVContentLightMetadata *clli = (AVContentLightMetadata *) side_data->data;
+        AV_WB32(s->buf, clli->MaxCLL * 10000);
+        AV_WB32(s->buf + 4, clli->MaxFALL * 10000);
+        png_write_chunk(&s->bytestream, MKTAG('c', 'L', 'L', 'i'), s->buf, 8);
+    }
+
+    side_data = av_frame_get_side_data(pict, AV_FRAME_DATA_MASTERING_DISPLAY_METADATA);
+    if (side_data) {
+        AVMasteringDisplayMetadata *mdvc = (AVMasteringDisplayMetadata *) side_data->data;
+        if (mdvc->has_luminance && mdvc->has_primaries) {
+            for (int i = 0; i < 3; i++) {
+                AV_WB16(s->buf + 2*i, PNG_Q2D(mdvc->display_primaries[i][0], 50000));
+                AV_WB16(s->buf + 2*i + 2, PNG_Q2D(mdvc->display_primaries[i][1], 50000));
+            }
+            AV_WB16(s->buf + 12, PNG_Q2D(mdvc->white_point[0], 50000));
+            AV_WB16(s->buf + 14, PNG_Q2D(mdvc->white_point[1], 50000));
+            AV_WB32(s->buf + 16, PNG_Q2D(mdvc->max_luminance, 10000));
+            AV_WB32(s->buf + 20, PNG_Q2D(mdvc->min_luminance, 10000));
+            png_write_chunk(&s->bytestream, MKTAG('m', 'D', 'V', 'c'), s->buf, 24);
+        }
+    }
+
     if (png_get_chrm(pict->color_primaries, s->buf))
         png_write_chunk(&s->bytestream, MKTAG('c', 'H', 'R', 'M'), s->buf, 32);
     if (png_get_gama(pict->color_trc, s->buf))
-- 
2.43.0