[FFmpeg-devel] [PATCH 4/4] avutil/channel_layout: fix av_channel_layout_describe_bprint with custom and ambisonic channels

[James Almer]

On 3/15/2022 5:30 PM, Marton Balint wrote:
> bp->len cannot be used to detect if try_describe_ambisonic was successful
> because the bprint buffer might contain other data as well.
> 
> Also describing an invalid ambisonic layout should not return 0 but
> AVERROR(EINVAL) instead, so change try_describe_ambisonic to actually return
> error on invalid ambisonics. This also allows us to fix the first issue.
> 
> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
>   libavutil/channel_layout.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/libavutil/channel_layout.c b/libavutil/channel_layout.c
> index 8406089fe0..be511dcf68 100644
> --- a/libavutil/channel_layout.c
> +++ b/libavutil/channel_layout.c
> @@ -687,14 +687,14 @@ static int ambisonic_order(const AVChannelLayout *channel_layout)
>   /**
>    * If the custom layout is n-th order standard-order ambisonic, with optional
>    * extra non-diegetic channels at the end, write its string description in bp.
> - * Return a negative error code on error.
> + * Return a negative error code otherwise.
>    */
>   static int try_describe_ambisonic(AVBPrint *bp, const AVChannelLayout *channel_layout)
>   {
>       int nb_ambi_channels;
>       int order = ambisonic_order(channel_layout);
>       if (order < 0)
> -        return 0;
> +        return order;
>   
>       av_bprintf(bp, "ambisonic %d", order);
>   
> @@ -736,7 +736,7 @@ int av_channel_layout_describe_bprint(const AVChannelLayout *channel_layout,
>       case AV_CHANNEL_ORDER_CUSTOM:
>           if (channel_layout->order == AV_CHANNEL_ORDER_CUSTOM) {
>               int res = try_describe_ambisonic(bp, channel_layout);
> -            if (res < 0 || bp->len)
> +            if (res >= 0)
>                   return res;

return 0. The doxy for av_channel_layout_describe_bprint() does not 
define values > 0.

>           }
>           if (channel_layout->nb_channels)