Re: [FFmpeg-devel] [PATCH] Added support for MB_INFO

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Anton Khirnov:
> Quoting Carotti, Elias (2022-06-21 10:48:07)
>> Hi,
>>
>> extending AVVideoEncParams was the first hypothesis I made but it
>> didn't seem it was the proper place to add the mb_info flags.
>>
>> I may be wrong but my impression is that AVVideoEncParams is used to
>> carry encoding parameters read from the bitstream at the decoder side
>> while here were going the other direction, i.e., were passing
>> information from the application to the encoder.
>>
>> Secondly, mb_info can't be strictly considered encoding parameters and
>> it's not present in the bitstream at all. 
>> It's just a way to give hints to the libx264 encoder on which
>> macroblock we know have not changed since the previous frame and could
>> be coded as P_SKIPs. Libx264 however, may or may not oblige according
>> to its logic, and this specific information is not transmitted in the
>> bitstream nor can be recovered at the decoder.
> 
> Right, seems I was too hasty in reading your patch.
> 
> But then I have to wonder whether this really needs a new installed
> header, with a struct and a destructor, given that it's specific to a
> single encoder for a single codec that is about 20 years old now.
> 
> Wouldn't AV_FRAME_DATA_X264_MBINFO that would be just a raw array of
> uint8_t serve your needs just as fine? You could even get custom buffer
> management by using AVFrameSideData.buf.
> 

There is one problem though: libx264's free functions don't accept an
opaque parameter, so one can't easily create a reference for libx264 to
unref. I don't see a way around duplicating this buffer in the encoder.
(Or is there a way to know when libx264 is done with using this buffer?)

- Andreas
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