Re: [FFmpeg-devel] [PATCH v2 4/4] avutil/channel_layout: fix av_channel_layout_describe_bprint with custom and ambisonic channels

[James Almer <jamrial@gmail.com>]

On 3/15/2022 6:18 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@passwd.hu>
> ---
>   libavutil/channel_layout.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/libavutil/channel_layout.c b/libavutil/channel_layout.c
> index fb1f72737f..1a141d4a6a 100644
> --- a/libavutil/channel_layout.c
> +++ b/libavutil/channel_layout.c
> @@ -689,14 +689,14 @@ 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);
>   
> @@ -739,8 +739,8 @@ 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)
> -                return res;
> +            if (res >= 0)
> +                return 0;
>           }
>           if (channel_layout->nb_channels)
>               av_bprintf(bp, "%d channels (", channel_layout->nb_channels);

LGTM.
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