[FFmpeg-devel] [PATCH v20 02/20] avutil/frame: Prepare AVFrame for subtitle handling

[Soft Works]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Hendrik
> Leppkes
> Sent: Monday, December 6, 2021 12:37 AM
> To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] [PATCH v20 02/20] avutil/frame: Prepare AVFrame
> for subtitle handling
> 
> On Mon, Dec 6, 2021 at 12:23 AM Soft Works <softworkz at hotmail.com> wrote:
> >
> > It can only work like that.
> >
> 
> You literally designed subtitle filtering. You defined how it works.
> All your explanations come down to some fancy form of "because I made
> it required".
> 
> All I'm hearing is that some internal mechanisms in avfilter need it.
> Why is it a public field in one of the most key structures in our
> entire codebase? You understand this concern, right? Any public field
> should first (and only) answer the question, what information does
> this convey to the user? Does the user need this information? I'm not
> seeing any of that in your explanations. All I'm seeing is internal
> avfilter workings - cemented in public API.
> 
> You are not integrating into an existing infrastructure, you are
> literally trying to add the whole thing, so you can change it to not
> need this redundant field.
> 
> - Hendrik

OK, maybe this is better to understand. Very simple burn-down:

I send a subtitle frame into a filtergraph.

pts = 10
subtitle_pts = 10

Now I need to re-send a duplicate of that frame into the graph
(=> heartbeat - to keep the graph flowing)

Now, it's not possible (by lavf design, not mine) to send another frame 
without increasing the pts of the frame. So we send it like this:

pts = 11
subtitle_pts = 10

The pts needs to be increased. But the start-display time of the 
subtitle event must not be changed - it's still the same frame like
before, just a duplicate.


softworkz