[FFmpeg-devel] [PATCH] libavutil: additional side_data accessor

[James Almer]

On 4/20/2021 7:10 AM, Nicolas George wrote:
> Brad Hards (12021-04-20):
>> The existing function allows access the first instance of a given
>> type. Mostly that is OK, but some types can occur multiple times
>> (e.g. libx264 can write version info, VANC and UMID related data as
>> user data unregistered SEI.
>>
>> This adds API to access additional instances of a given SEI type.
>> ---
>>   libavutil/frame.c | 19 +++++++++++++++++++
>>   libavutil/frame.h | 20 ++++++++++++++++++++
>>   2 files changed, 39 insertions(+)
> 
> IIRC, there was a discussion a long time ago that concluded that
> multiple instances of the same side data should not happen.
> 
> Somebody remembers it?

I recall long ago i tried to make av_frame_new_side_data() replace the 
existing element if it found one, effectively limiting side data to one 
per type and copying the behavior of packet side data, but it was 
rejected as it was argued more than one per type had some use. And 
seeing that now decoders like h264 may attach more than one element of 
AV_FRAME_DATA_SEI_UNREGISTERED type as contained inside the bitstream 
AUs, it may be a good idea for it to be supported officially with our 
accessors (Right now you need to manually traverse the side data array 
to find all instances of a given type).

> 
> Regards,
> 
> 
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