Re: [FFmpeg-devel] [PATCH] avfilter/formats: set audio fmt lists for vaf filters

[Niklas Haas <ffmpeg@haasn.xyz>]

On Thu, 14 Dec 2023 15:39:11 +0100 Niklas Haas <ffmpeg@haasn.xyz> wrote:
> From: Niklas Haas <git@haasn.dev>
> 
> Currently, the logic inside the FF_FILTER_FORMATS_QUERY_FUNC branch
> prevents this code from running in the event that we have a filter with
> a single video input and a single audio output, as the resulting audio
> output link will not have its channel counts / samplerates correctly
> initialized to their default values, possibly triggering a segfault
> downstream.
> 
> An example of such a filter is vaf_spectrumsynth. Although this
> particular filter already sets up the channel counts and samplerates as
> part of the query function and therefore avoids triggering this bug, the
> bug still exists in principle. (And importantly, sets a wrong precedent)
> ---
>  libavfilter/formats.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/libavfilter/formats.c b/libavfilter/formats.c
> index d1c97daf64..114886aeb2 100644
> --- a/libavfilter/formats.c
> +++ b/libavfilter/formats.c
> @@ -808,16 +808,17 @@ int ff_default_query_formats(AVFilterContext *ctx)
>      /* Intended fallthrough */
>      case FF_FILTER_FORMATS_PASSTHROUGH:
>      case FF_FILTER_FORMATS_QUERY_FUNC:
> -        type    = ctx->nb_inputs  ? ctx->inputs [0]->type :
> -                  ctx->nb_outputs ? ctx->outputs[0]->type : AVMEDIA_TYPE_VIDEO;
> -        formats = ff_all_formats(type);
> +        type = AVMEDIA_TYPE_UNKNOWN;
> +        formats = ff_all_formats(ctx->nb_inputs  ? ctx->inputs [0]->type :
> +                                 ctx->nb_outputs ? ctx->outputs[0]->type :
> +                                 AVMEDIA_TYPE_VIDEO);
>          break;
>      }
>  
>      ret = ff_set_common_formats(ctx, formats);
>      if (ret < 0)
>          return ret;
> -    if (type == AVMEDIA_TYPE_AUDIO) {
> +    if (type != AVMEDIA_TYPE_VIDEO) {
>          ret = ff_set_common_all_channel_counts(ctx);
>          if (ret < 0)
>              return ret;
> -- 
> 2.43.0
> 

This patch fixes the underlying issue (alongside the corresponding
adjustment to the conditional from `type == AVMEDIA_TYPE_VIDEO` to `type
!= AVMEDIA_TYPE_AUDIO` in patch 03/15).
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