[FFmpeg-devel] [PATCH] avcodec/pngdec: do not blend on transparent black

[Benoit Fouet]

There is no need to memset the zlib output buffer, as there is no
blending happening there. Instead, do not blend when the dispose
operation is set to 'background' (tranparent black).
---
 libavcodec/pngdec.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index 4c9d321..da852c4 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -674,10 +674,6 @@ static int decode_idat_chunk(AVCodecContext *avctx, PNGDecContext *s,
         s->crow_buf          = s->buffer + 15;
         s->zstream.avail_out = s->crow_size;
         s->zstream.next_out  = s->crow_buf;
-
-        if (avctx->codec_id == AV_CODEC_ID_APNG &&
-            s->dispose_op == APNG_DISPOSE_OP_BACKGROUND)
-            memset(s->zstream.next_out, 0, s->zstream.avail_out);
     }
     s->state |= PNG_IDAT;
     if ((ret = png_decode_idat(s, length)) < 0)
@@ -887,7 +883,7 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
         pd_last += s->image_linesize;
     }
 
-    if (s->blend_op == APNG_BLEND_OP_OVER) {
+    if (s->dispose_op != APNG_DISPOSE_OP_BACKGROUND && s->blend_op == APNG_BLEND_OP_OVER) {
         uint8_t ri, gi, bi, ai;
 
         if (avctx->pix_fmt == AV_PIX_FMT_RGBA) {
-- 
2.2.0.rc2.23.gca0107e