[FFmpeg-devel] [PATCH 1/2] avcodec/ac3dec: don't export Matrix Encoding side data when no such info is coded

[FFmpeg-devel] [PATCH 1/2] avcodec/ac3dec: don't export Matrix Encoding side data when no such info is coded

[James Almer]

No point inserting the side data to all frames just to say there's no
coded matrix encoding.

Signed-off-by: James Almer <jamrial@gmail.com>
---
 libavcodec/ac3dec.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index 0b120e6140..7a84f3c85d 100644
--- a/libavcodec/ac3dec.c
+++ b/libavcodec/ac3dec.c
@@ -1819,7 +1819,8 @@ skip:
             break;
         }
     }
-    if ((ret = ff_side_data_update_matrix_encoding(frame, matrix_encoding)) < 0)
+    if (matrix_encoding != AV_MATRIX_ENCODING_NONE &&
+        (ret = ff_side_data_update_matrix_encoding(frame, matrix_encoding)) < 0)
         return ret;
 
     /* AVDownmixInfo */
-- 
2.39.0

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[FFmpeg-devel] [PATCH 2/2] avcodec/ac3dec: export downmix info side data only when no downmix is done by the decoder

[James Almer]

Same as with Matrix Encoding, add a check to ensure the decoder is not
doing a downmix of its own.

Signed-off-by: James Almer <jamrial@gmail.com>
---
 libavcodec/ac3dec.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index 7a84f3c85d..722a1028b7 100644
--- a/libavcodec/ac3dec.c
+++ b/libavcodec/ac3dec.c
@@ -1824,7 +1824,11 @@ skip:
         return ret;
 
     /* AVDownmixInfo */
-    if ((downmix_info = av_downmix_info_update_side_data(frame))) {
+    if (s->channel_mode == (s->output_mode & ~AC3_OUTPUT_LFEON)) {
+        downmix_info = av_downmix_info_update_side_data(frame);
+        if (!downmix_info)
+            return AVERROR(ENOMEM);
+
         switch (s->preferred_downmix) {
         case AC3_DMIXMOD_LTRT:
             downmix_info->preferred_downmix_type = AV_DOWNMIX_TYPE_LTRT;
@@ -1847,8 +1851,7 @@ skip:
             downmix_info->lfe_mix_level       = gain_levels_lfe[s->lfe_mix_level];
         else
             downmix_info->lfe_mix_level       = 0.0; // -inf dB
-    } else
-        return AVERROR(ENOMEM);
+    }
 
     *got_frame_ptr = 1;
 
-- 
2.39.0

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Re: [FFmpeg-devel] [PATCH 1/2] avcodec/ac3dec: don't export Matrix Encoding side data when no such info is coded

[Andreas Rheinhardt]

James Almer:
> No point inserting the side data to all frames just to say there's no
> coded matrix encoding.
> 
> Signed-off-by: James Almer <jamrial@gmail.com>
> ---
>  libavcodec/ac3dec.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
> index 0b120e6140..7a84f3c85d 100644
> --- a/libavcodec/ac3dec.c
> +++ b/libavcodec/ac3dec.c
> @@ -1819,7 +1819,8 @@ skip:
>              break;
>          }
>      }
> -    if ((ret = ff_side_data_update_matrix_encoding(frame, matrix_encoding)) < 0)
> +    if (matrix_encoding != AV_MATRIX_ENCODING_NONE &&
> +        (ret = ff_side_data_update_matrix_encoding(frame, matrix_encoding)) < 0)
>          return ret;
>  
>      /* AVDownmixInfo */

If the preceding frame had a nontrivial matrix encoding, will users
think that the matrix encoding from the last frame still persists?

- Andreas

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Re: [FFmpeg-devel] [PATCH 1/2] avcodec/ac3dec: don't export Matrix Encoding side data when no such info is coded

[James Almer]

On 1/13/2023 4:09 AM, Andreas Rheinhardt wrote:
> James Almer:
>> No point inserting the side data to all frames just to say there's no
>> coded matrix encoding.
>>
>> Signed-off-by: James Almer <jamrial@gmail.com>
>> ---
>>   libavcodec/ac3dec.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
>> index 0b120e6140..7a84f3c85d 100644
>> --- a/libavcodec/ac3dec.c
>> +++ b/libavcodec/ac3dec.c
>> @@ -1819,7 +1819,8 @@ skip:
>>               break;
>>           }
>>       }
>> -    if ((ret = ff_side_data_update_matrix_encoding(frame, matrix_encoding)) < 0)
>> +    if (matrix_encoding != AV_MATRIX_ENCODING_NONE &&
>> +        (ret = ff_side_data_update_matrix_encoding(frame, matrix_encoding)) < 0)
>>           return ret;
>>   
>>       /* AVDownmixInfo */
> 
> If the preceding frame had a nontrivial matrix encoding, will users
> think that the matrix encoding from the last frame still persists?

Yeah, i thought about it after i sent this when i was looking into ways 
to use this info in swr, so I'm withdrawing this patch (not the second).

> 
> - Andreas
> 
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