[FFmpeg-devel] [PATCH] fftools/ffmpeg_opt: try to propagate the requested output channel layout

[James Almer]

On 8/21/2022 5:42 PM, James Almer wrote:
> Don't silently replace it with the default layout for the amount of channels
> from the requested layout.
> 
> Should fix ticket #9869
> 
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>   fftools/ffmpeg_opt.c | 38 +++++++++++++++++++++++++++++++++++++-
>   1 file changed, 37 insertions(+), 1 deletion(-)
> 
> diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
> index 30ca5cd609..3a555c4c16 100644
> --- a/fftools/ffmpeg_opt.c
> +++ b/fftools/ffmpeg_opt.c
> @@ -2865,6 +2865,42 @@ static void of_add_metadata(AVFormatContext *oc, const OptionsContext *o)
>           }
>       }
>   }
> +static void set_channel_layout(OutputFilter *f, OutputStream *ost)
> +{
> +    int i, err;
> +
> +    if (ost->enc_ctx->ch_layout.order != AV_CHANNEL_ORDER_UNSPEC) {
> +        /* Pass the layout through for all orders but UNSPEC */
> +        err = av_channel_layout_copy(&f->ch_layout, &ost->enc_ctx->ch_layout);
> +        if (err < 0)
> +            exit_program(1);
> +        return;
> +    }
> +
> +    /* Requested layout is of order UNSPEC */
> +    if (!ost->enc->ch_layouts) {
> +        /* Use the default native layout for the requested amount of channels when the
> +           encoder doesn't have a list of supported layouts */
> +        av_channel_layout_default(&f->ch_layout, ost->enc_ctx->ch_layout.nb_channels);
> +        return;
> +    }
> +    /* Encoder has a list of supported layouts. Pick the first layout in it with the
> +       same amount of channels as the requested layout */
> +    for (i = 0; ost->enc->ch_layouts[i].nb_channels; i++) {
> +        if (ost->enc->ch_layouts[i].nb_channels == ost->enc_ctx->ch_layout.nb_channels)
> +            break;
> +    }
> +    if (ost->enc->ch_layouts[i].nb_channels) {
> +        /* Use it if one is found */
> +        err = av_channel_layout_copy(&f->ch_layout, &ost->enc->ch_layouts[i]);
> +        if (err < 0)
> +            exit_program(1);
> +        return;
> +    }
> +    /* If no layout for the amount of channels requested was found, use the default
> +       native layout for it. */
> +    av_channel_layout_default(&f->ch_layout, ost->enc_ctx->ch_layout.nb_channels);
> +}
>   
>   static int open_output_file(OptionsContext *o, const char *filename)
>   {
> @@ -3055,7 +3091,7 @@ static int open_output_file(OptionsContext *o, const char *filename)
>                       f->sample_rates = ost->enc->supported_samplerates;
>                   }
>                   if (ost->enc_ctx->ch_layout.nb_channels) {
> -                    av_channel_layout_default(&f->ch_layout, ost->enc_ctx->ch_layout.nb_channels);
> +                    set_channel_layout(f, ost);
>                   } else if (ost->enc->ch_layouts) {
>                       f->ch_layouts = ost->enc->ch_layouts;
>                   }

Will apply soon.