[FFmpeg-devel] [PATCH] avfilter/vf_stereo3d: implement auto detection by using frame side data

[wm4]

On Fri, 1 Dec 2017 18:02:52 +0100
Michael Niedermayer <michael at niedermayer.cc> wrote:

> On Fri, Dec 01, 2017 at 10:01:42AM +0100, Nicolas George wrote:
> > Paul B Mahol (2017-11-30):  
> > > +static int reset_links(AVFilterContext *filter)
> > > +{
> > > +    int i, ret;
> > > +
> > > +    if (!filter)
> > > +        return 0;
> > > +
> > > +    for (i = 0; i < filter->nb_outputs; i++) {
> > > +        AVFilterLink *link = filter->outputs[i];
> > > +
> > > +        link->init_state = AVLINK_UNINIT;
> > > +        link->frame_rate.num = link->frame_rate.den = 0;
> > > +        link->w = link->h = 0;
> > > +
> > > +        ret = reset_links(link->dst);
> > > +        if (ret < 0)
> > > +            return ret;
> > > +    }
> > > +
> > > +    if (!i)
> > > +        return avfilter_config_links(filter);
> > > +
> > > +    return 0;
> > > +}  
> > 
> > Sorry, but no. All filters are currently written with the assumption
> > that config_props is called only once. Not all of them actually rely on
> > this assumption, but some do, and expect the fields of the private
> > context to be in their initial state. Violating that assumption would
> > result in a lot of memory leaks and probably a few crashes, some of them
> > security relevant.
> > 
> > Plus, the public API of buffersink does not document params changes and
> > does not provide a good way of reacting to it, so enabling params
> > changes like that would have problematic results on applications that
> > expect frames with all the same size.
> > 
> > (By the way, I am quite worried to see that Michael weakened the
> > protections for that last point in 5d859e59809.)
> >   
> 
> > Filters reconfiguration has been wanted for a lot of time. If it was
> > that simple, it would have been done already. If you want to implement
> > it, please go ahead, but it will not be an easy task.  
> 
> As the one who tried implementing changing frame parameters like
> dimension long time ago, the only real problem i encountered was
> bikeshedding, i dont rememer a technical problem. The bikeshedding in
> fact resolved itself but by the time i had lost interrest ...
> 
> And in fact many filters should just be able to handle changing frame
> parameters as they are or with minimal changes.

Well, the result is that at least the vf_scale filter appears to
blatantly violate the API and crashes my software.