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

[Nicolas George]

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.

Regards,

-- 
  Nicolas George
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