[FFmpeg-devel] [PATCH v2] lavu/avframe: add a time_base field

[Anton Khirnov]

Quoting Lynne (2021-11-26 09:00:59)
> 25 Nov 2021, 23:49 by cus at passwd.hu:
> 
> >
> >
> > On Thu, 25 Nov 2021, Lynne wrote:
> >
> >> This adds a time_base field (currently unused), analogue to the
> >> AVPacket.time_base field.
> >> This allows for API clients to exchange AVFrames directly, without
> >> needing to plumb extra data from sources via side mechanisms.
> >>
> >
> > The objections raised before still stand I believe, and again, the main concern is that the API user won't know when to use the packet or frame timebase and when to use the frame/packet source timebase.
> >
> > You write this in the doxy:
> >
> >> Time base for the timestamps in this frame. May be 0, in which case the
> >> time_base from the frame source should be used.
> >>
> >
> > One could easily think - based on this text alone - that every user of avcodec_receive_frame should check if AVFrame->time_base is 0 to calculate real PTS...
> >
> > I'd be a lot more willing to accept this if you could document explicitly that AVFrame->time_base (and AVPacket->time_base) is not used by the API right now, and is similar to e.g. *opaque field. And later, if by using some magic flag or new API or whatever it turns out to make sense to actually use AVPacket/AVFrame time base, the doxy text can be extended accordingly.
> >
> 
> So you'd like for the field to either be fully opaque or fully working (by always
> having the correct time_base value)?
> That sounds fair, description changed:
> "Time base for the timestamps in this frame. Currently unused by any API,
> users can set this and use it as an opaque field. In the future, this field may
> be set by the API for you, but its value will always be ignored."

Always is a bit too strong, presumably we do want to start using that
field eventually.

How about something like:
In the future, this field may be set on frames output by decoders or
filters, but its value will be by default ignored on input to encoders
or filters.

-- 
Anton Khirnov