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in repository ffmpeg.

commit c717827955ae7b996923fe6952ad5699b84af4bd
Author:     Ayoub Nabil Boubagrat 
<[email protected]>
AuthorDate: Thu Aug 6 13:46:44 2026 +0200
Commit:     James Almer <[email protected]>
CommitDate: Fri Aug 7 02:33:33 2026 +0000

    swresample/rematrix: use unity gain for top-front downmix
    
    ITU-R BS.2127-1 maps U+030 and U-030 to the matching ear-level front 
channels at unity gain.
    
    the current matrix uses 0.707 when the input also contains front channels. 
use 1.0 instead.
    
    Signed-off-by: Ayoub Nabil Boubagrat 
<[email protected]>
---
 libswresample/rematrix.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/libswresample/rematrix.c b/libswresample/rematrix.c
index 6f4c16ee45..77ec2250a6 100644
--- a/libswresample/rematrix.c
+++ b/libswresample/rematrix.c
@@ -287,13 +287,9 @@ static void build_matrix(const AVChannelLayout 
*in_ch_layout, const AVChannelLay
             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);
         } 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;
-                matrix[FRONT_RIGHT][TOP_FRONT_RIGHT] += M_SQRT1_2;
-            } else {
-                matrix[FRONT_LEFT ][TOP_FRONT_LEFT ] += 1.0;
-                matrix[FRONT_RIGHT][TOP_FRONT_RIGHT] += 1.0;
-            }
+            /* U+030 -> M+030 in ITU-R BS.2127-1, Table 16. */
+            matrix[FRONT_LEFT ][TOP_FRONT_LEFT ] += 1.0;
+            matrix[FRONT_RIGHT][TOP_FRONT_RIGHT] += 1.0;
         } else if (av_channel_layout_index_from_channel(out_ch_layout, 
AV_CHAN_FRONT_CENTER) >= 0) {
             matrix[FRONT_CENTER][TOP_FRONT_LEFT ] += M_SQRT1_2;
             matrix[FRONT_CENTER][TOP_FRONT_RIGHT] += M_SQRT1_2;

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