Re: [FFmpeg-devel] [PATCH 3/4] avutil/channel_layout: do not copy alloc new map for extra channel layout

[James Almer <jamrial@gmail.com>]

On 3/15/2022 5:30 PM, Marton Balint wrote:
> Also use av_channel_layout_bprint directly for describing channel layout for
> extra channels.
> 
> Signed-off-by: Marton Balint <cus@passwd.hu>
> ---
>   libavutil/channel_layout.c | 16 +++-------------
>   1 file changed, 3 insertions(+), 13 deletions(-)
> 
> diff --git a/libavutil/channel_layout.c b/libavutil/channel_layout.c
> index fb2335a334..8406089fe0 100644
> --- a/libavutil/channel_layout.c
> +++ b/libavutil/channel_layout.c
> @@ -702,29 +702,19 @@ static int try_describe_ambisonic(AVBPrint *bp, const AVChannelLayout *channel_l
>       nb_ambi_channels = (order + 1) * (order + 1);
>       if (nb_ambi_channels < channel_layout->nb_channels) {
>           AVChannelLayout extra = { 0 };
> -        char buf[128];
>   
>           if (channel_layout->order == AV_CHANNEL_ORDER_AMBISONIC) {
>               extra.order       = AV_CHANNEL_ORDER_NATIVE;
>               extra.nb_channels = av_popcount64(channel_layout->u.mask);
>               extra.u.mask      = channel_layout->u.mask;
>           } else {
> -            const AVChannelCustom *map = channel_layout->u.map;
> -
>               extra.order       = AV_CHANNEL_ORDER_CUSTOM;
>               extra.nb_channels = channel_layout->nb_channels - nb_ambi_channels;
> -            extra.u.map       = av_calloc(extra.nb_channels, sizeof(*extra.u.map));
> -            if (!extra.u.map)
> -                return AVERROR(ENOMEM);
> -
> -            memcpy(extra.u.map, &map[nb_ambi_channels],
> -                   sizeof(*extra.u.map) * extra.nb_channels);
> +            extra.u.map       = channel_layout->u.map + nb_ambi_channels;
>           }
>   
> -        av_channel_layout_describe(&extra, buf, sizeof(buf));
> -        av_channel_layout_uninit(&extra);

Maybe add a comment that you're not calling uninit on extra because it 
doesn't own its AVChannelMap pointer.

> -
> -        av_bprintf(bp, "+%s", buf);
> +        av_bprint_chars(bp, '+', 1);
> +        av_channel_layout_describe_bprint(&extra, bp);
>       }
>   
>       return 0;
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