[FFmpeg-devel] [PATCH] apng: fix rgb24 blending bug for non-alpha frames

[Hassan Hany via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

From: "U-DESKTOP-70DF2U5\\GIGABYT" <hassanhanyrashad@gmail.com>

Delta frame optimization in APNG encoder caused gray bars for RGB24 frames.
This patch disables delta optimization for non-alpha frames, ensuring correct
rendering. Delta optimization is preserved for RGBA frames.

Fixes: trac Ticket #9602

Signed-off-by: U-DESKTOP-70DF2U5\GIGABYT <hassanhanyrashad@gmail.com>
---
This bug caused visible artifacts such as gray bars in non-alpha 
pixel formats such as RGB24 or GRAY. This patch disabled delta frame
optimization only for non alpha channels. the output size increased
from 512kb to 1.1mb on the test sample but correctness was restored
and the relevant APNG FATE tests were ran and no regression occurred
 libavcodec/pngenc.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/libavcodec/pngenc.c b/libavcodec/pngenc.c
index e627bf83fc..3e46363b00 100644
--- a/libavcodec/pngenc.c
+++ b/libavcodec/pngenc.c
@@ -39,7 +39,7 @@
 #include "libavutil/opt.h"
 #include "libavutil/rational.h"
 #include "libavutil/stereo3d.h"
-
+#include "libavutil/pixdesc.h"
 #include <zlib.h>
 
 #define IOBUF_SIZE 4096
@@ -894,6 +894,19 @@ static int apng_encode_frame(AVCodecContext *avctx, const AVFrame *pict,
         best_fctl_chunk->blend_op = APNG_BLEND_OP_SOURCE;
         return encode_frame(avctx, pict);
     }
+    
+    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(pict->format);
+        
+    if(!(desc->flags & AV_PIX_FMT_FLAG_ALPHA)){
+         best_fctl_chunk->width = pict->width;
+         best_fctl_chunk->height = pict->height;
+         best_fctl_chunk->x_offset = 0;
+         best_fctl_chunk->y_offset = 0;
+         best_fctl_chunk->blend_op = APNG_BLEND_OP_SOURCE;
+         best_fctl_chunk->dispose_op = APNG_DISPOSE_OP_NONE;
+          return encode_frame(avctx, pict);
+         } 
+    
 
     diffFrame = av_frame_alloc();
     if (!diffFrame)
-- 
2.52.0

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