[FFmpeg-devel] [PATCH] swresample/rematrix: fix mixing of center channels

[James Almer]

With this, the output from

ffmpeg -i $fate-samples/ac3/monsters_inc_5.1_448_small.ac3 -af aresample,aformat=channel_layouts=mono -f s16le -

matches the one from

ffmpeg -downmix mono -i $fate-samples/ac3/monsters_inc_5.1_448_small.ac3 -f s16le -

When testing with tiny_psnr.

Signed-off-by: James Almer <jamrial at gmail.com>
---
 libswresample/rematrix.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libswresample/rematrix.c b/libswresample/rematrix.c
index b9bf4dcac0..e4dc61d6db 100644
--- a/libswresample/rematrix.c
+++ b/libswresample/rematrix.c
@@ -217,7 +217,7 @@ av_cold int swr_build_matrix2(const AVChannelLayout *in_layout, const AVChannelL
             matrix[FRONT_CENTER][ FRONT_LEFT]+= M_SQRT1_2;
             matrix[FRONT_CENTER][FRONT_RIGHT]+= M_SQRT1_2;
             if (av_channel_layout_index_from_channel(&in_ch_layout, AV_CHAN_FRONT_CENTER) >= 0)
-                matrix[FRONT_CENTER][ FRONT_CENTER] = center_mix_level*sqrt(2);
+                matrix[FRONT_CENTER][ FRONT_CENTER] += M_SQRT1_2;
         }else
             av_assert0(0);
     }
@@ -334,7 +334,7 @@ av_cold int swr_build_matrix2(const AVChannelLayout *in_layout, const AVChannelL
             matrix[TOP_FRONT_CENTER][TOP_FRONT_LEFT ] += M_SQRT1_2;
             matrix[TOP_FRONT_CENTER][TOP_FRONT_RIGHT] += M_SQRT1_2;
             if (av_channel_layout_index_from_channel(&in_ch_layout, AV_CHAN_TOP_FRONT_CENTER) >= 0)
-                matrix[TOP_FRONT_CENTER][TOP_FRONT_CENTER] = center_mix_level * sqrt(2);
+                matrix[TOP_FRONT_CENTER][TOP_FRONT_CENTER] += M_SQRT1_2;
         } else if (av_channel_layout_index_from_channel(&out_ch_layout, AV_CHAN_FRONT_LEFT) >= 0) {
             if (av_channel_layout_index_from_channel(&in_ch_layout, AV_CHAN_FRONT_LEFT) >= 0) {
                 matrix[FRONT_LEFT ][TOP_FRONT_LEFT ] += M_SQRT1_2;
-- 
2.47.1