[FFmpeg-devel] [PATCH] avformat: add apic to AVStream

[James Almer]

On 3/29/2021 10:46 AM, James Almer wrote:
> On 3/29/2021 10:20 AM, Nicolas George wrote:
>> James Almer (12021-03-29):
>>> Can this be done? id3v2 attached pics for many formats are handled by 
>>> the
>>> generic demux code in avformat_open_input() and not by the actual 
>>> demuxer.
>>> And in demuxers like asf, it seems to be done in read_header().
>>> Would seeking be able to fetch these pictures again? The comment in the
>>> AV_DISPOSITION_ATTACHED_PIC doxy makes me think it's not possible.
>>>
>>> Personally, even if possible i think triggering a seek just to fetch an
>>> attachment is inefficient and disruptive to the user's demuxing/decoding
>>> process, and a step backwards considering it used to always be 
>>> available,
>>> for both seekable and non-seekable input, the latter which will no 
>>> longer be
>>> able to access the picture past the original packet.
>>
>> As I said, at worse it accesses a field just like now. So of course it
>> can be done.
>>
>> The point is that having a function to get the packet rather than just a
>> pointer gives us more freedom to extend the API later.
> 
> Not against it in that case, even if it will probably never stop just 
> being an abstraction layer to fetch an always available packet, but know 
> that this will kill Andreas' idea of defining how the (until now) public 
> packet can be used to simplify attached pics in muxing scenarios, or 
> make it considerably more complex to the point it's no longer worth it.

Some people on IRC mentioned the possibility of adding a demuxer option 
to disable fetching/storing attached pictures. The streams would not be 
allocated at all in that case. Would that be ok?