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

[James Almer]

On 1/13/2025 12:49 AM, Michael Niedermayer wrote:

Hi James

On Sun, Jan 12, 2025 at 06:52:55PM -0300, James Almer wrote:

On 1/12/2025 6:25 PM, Michael Niedermayer wrote:

Hi

On Sat, Jan 11, 2025 at 11:13:30AM -0300, James Almer wrote:

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 <jamr...@gmail.com>
---
   libswresample/rematrix.c | 4 ++--
   1 file changed, 2 insertions(+), 2 deletions(-)

This worsense test results:

What test is this, and how is it read?

its just tests/swresample

and a dumb script that tries to compare its output to spot cases that worsen

Is this any better? (Also makes the above command line match)

diff --git a/libswresample/rematrix.c b/libswresample/rematrix.c
index b9bf4dcac0..af89c30451 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] += 
center_mix_level*sqrt(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] += center_mix_level 
* sqrt(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;

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