[FFmpeg-devel] [PATCH] avcodec/png{dec, enc}: update mDCV and cLLI chunk capitalization

[Leo Izen]

The PNGv3 Specification Draft [1] has changed the capitalization
of mDCV and cLLI chunks (formerly mDCv and cLLi). This patch updates
FFmpeg to work with the new chunk names while retaining decode-side
compatibility with files created using the old names.

[1]: https://w3c.github.io/png/

Signed-off-by: Leo Izen <leo.izen at gmail.com>
---
 libavcodec/pngdec.c     | 12 +++++++-----
 libavcodec/pngenc.c     |  4 ++--
 tests/ref/fate/png-mdcv |  2 +-
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index c5b32c166d..f8cb61775e 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -757,7 +757,7 @@ static int populate_avctx_color_fields(AVCodecContext *avctx, AVFrame *frame)
         if (clli) {
             /*
              * 0.0001 divisor value
-             * see: https://www.w3.org/TR/png-3/#cLLi-chunk
+             * see: https://www.w3.org/TR/png-3/#cLLI-chunk
              */
             clli->MaxCLL = s->clli_max / 10000;
             clli->MaxFALL = s->clli_avg / 10000;
@@ -1566,18 +1566,20 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
 
             break;
         }
-        case MKTAG('c', 'L', 'L', 'i'):
+        case MKTAG('c', 'L', 'L', 'i'): /* legacy spelling, for backwards compat */
+        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));
+                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', 'C', 'v'):
+        case MKTAG('m', 'D', 'C', 'v'): /* legacy spelling, for backward compat */
+        case MKTAG('m', 'D', 'C', 'V'):
             if (bytestream2_get_bytes_left(&gb_chunk) != 24) {
-                av_log(avctx, AV_LOG_WARNING, "Invalid mDCv chunk size: %d\n", bytestream2_get_bytes_left(&gb_chunk));
+                av_log(avctx, AV_LOG_WARNING, "Invalid mDCV chunk size: %d\n", bytestream2_get_bytes_left(&gb_chunk));
                 break;
             }
             s->have_mdcv = 1;
diff --git a/libavcodec/pngenc.c b/libavcodec/pngenc.c
index cb79c04e11..37e8d5bfcf 100644
--- a/libavcodec/pngenc.c
+++ b/libavcodec/pngenc.c
@@ -445,7 +445,7 @@ static int encode_headers(AVCodecContext *avctx, const AVFrame *pict)
         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);
+        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);
@@ -460,7 +460,7 @@ static int encode_headers(AVCodecContext *avctx, const AVFrame *pict)
             AV_WB16(s->buf + 14, PNG_Q2D(mdcv->white_point[1], 50000));
             AV_WB32(s->buf + 16, PNG_Q2D(mdcv->max_luminance, 10000));
             AV_WB32(s->buf + 20, PNG_Q2D(mdcv->min_luminance, 10000));
-            png_write_chunk(&s->bytestream, MKTAG('m', 'D', 'C', 'v'), s->buf, 24);
+            png_write_chunk(&s->bytestream, MKTAG('m', 'D', 'C', 'V'), s->buf, 24);
         }
     }
 
diff --git a/tests/ref/fate/png-mdcv b/tests/ref/fate/png-mdcv
index c524a94ded..4328c56349 100644
--- a/tests/ref/fate/png-mdcv
+++ b/tests/ref/fate/png-mdcv
@@ -1,4 +1,4 @@
-fc68fe6c8c72343b96d2695f6913995b *tests/data/fate/png-mdcv.image2pipe
+b1837f5557ad969a3f9763840480d5c0 *tests/data/fate/png-mdcv.image2pipe
 439248 tests/data/fate/png-mdcv.image2pipe
 #tb 0: 1/25
 #media_type 0: video
-- 
2.47.1