>> @@ -3562,12 +3562,14 @@ static int init_output_stream(OutputStream *ost, 
>> char *error, int error_len)
>>              int i;
>>              for (i = 0; i < ist->st->nb_side_data; i++) {
>>                  AVPacketSideData *sd = &ist->st->side_data[i];
>> +                if (sd->type != AV_PKT_DATA_CPB_PROPERTIES) {
>>                  uint8_t *dst = av_stream_new_side_data(ost->st, sd->type, 
>> sd->size);
>>                  if (!dst)
>>                      return AVERROR(ENOMEM);
>>                  memcpy(dst, sd->data, sd->size);
>>                  if (ist->autorotate && sd->type == 
>> AV_PKT_DATA_DISPLAYMATRIX)
>>                      av_display_rotation_set((uint32_t *)dst, 0);
>> +                }
>>              }
>>          }
>>
>
>Can you clarify why you are exlcuding CBP side-data from being copied here? It 
>seems to not match the commit message in my mind.
>Note that from some containers, namely mov/mp4, the container can actually 
>provide CBP data, which means the stream CBP data would be valid and 
>potentially relevant.

This portion of the code is for when the stream is transcoded, so there is no 
relation between the input and output CPB.
But in init_output_stream_streamcopy() you can see that all side data is 
actually copied (it was already there, before this patchset, and I left it 
untouched) with no exception (=incl. CPB). And this is what I was looking for: 
being able to forward the input CPB size to the output, when stream-copying.

Note I only modified the CPB behaviour to restrict the scope of this patchset, 
but there are certainly other side data that should not be forwarded from input 
to output; this does not sound easy for me and maybe it should be discussed, 
but this patchset is consistent as is and I think it would require other 
patches if we want something more generic about what side data should be 
forwarded or not.

This is my understanding and I may have missed something of course. I have 
mainly tested mpeg2 encoding and stream-copying and checked fate.

Nicolas

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