[FFmpeg-devel] [PATCH] avpacket: RFC for ABI bump additions

[Anton Khirnov]

Quoting James Almer (2021-01-26 17:07:28)
> On 1/26/2021 1:02 PM, Anton Khirnov wrote:
> > Quoting Lynne (2021-01-24 18:34:36)
> >>>>
> >>>> Some devs (JEEB) wanted reception timestamps and original, overflowed timestamps for MPEG-TS.
> >>>> I'd be willing to add a reception timestamp as long as we add an additional time_base field
> >>>> and make it independent of the packet's pts field, since those timestamps are usually on
> >>>> highly precise system clock time bases, and reducing their precision would be undesirable.
> >>>>
> >>>
> >>> This sounds like side data to me.
> >>>
> >>>>
> >>>> I'm not sure about overflowed original timestamps or how they would help.
> >>>> Perhaps we should introduce an AVBufferRef *internal_ref like with AVFrame to
> >>>> store such single library-only data?
> >>>>
> >>>
> >>> I don't like treating the libraries specially, so -1 for me.
> >>> internal_ref should not exist either.
> >>>
> >>
> >> Yeah, tbh it's a single-library only field in avframes and is mainly used
> >> for hardware API weirdness reasons.
> > 
> > It's not even necessary, that code can work without it.
> > 
> >> Also another suggestion: should we add a few dozen bytes of padding at
> >> the end of the avpacket structure so if anything were to happen
> >> we wouldn't be block on waiting for a bump to add a field?
> > 
> > Ugly, but I guess acceptable? Have to be pretty careful what you add
> > though.
> 
> Alternatively, we could follow through with the idea of making its size 
> stop being part of the ABI.
> It's a big change since AVPacket is kinda advertised as one of the few 
> structs with ABI-tied size, and it wont happen until at least two years 
> from now. But now that the old deprecated decode/encode API is being 
> removed and non reference counted packets will no longer be a thing, 
> it's probably a good time to do it.

We could start by adding a field to AVPacket that would be set to a
magic value by av_packet_alloc().
Then have e.g. AVCodecContext/AVFormatContext warn when they see a
packet without this magic value.

-- 
Anton Khirnov