Re: [FFmpeg-devel] [PATCH 01/17] avcodec/ac3enc: Don't presume ch_layout to be AV_CHANNEL_ORDER_NATIVE

[James Almer <jamrial@gmail.com>]

On 4/7/2024 5:39 PM, Andreas Rheinhardt wrote:
> It is perfectly legal for users to use a custom layout
> that is equivalent to a supported native one.

Is that really the case? FFCodec.p.ch_layouts[] has a list of native 
ones, and the generic encode.c code will reject anything not in it.

I guess the encode.c check could be improved with 
av_channel_layout_retype().

> In this case the union in AVChannelLayout is not an uint64_t mask,
> but a pointer to a custom map.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>   libavcodec/ac3enc.c | 6 +-----
>   1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/libavcodec/ac3enc.c b/libavcodec/ac3enc.c
> index 7a6bcf7900..dc197c1517 100644
> --- a/libavcodec/ac3enc.c
> +++ b/libavcodec/ac3enc.c
> @@ -2192,18 +2192,14 @@ av_cold int ff_ac3_encode_close(AVCodecContext *avctx)
>   static av_cold int set_channel_info(AVCodecContext *avctx)
>   {
>       AC3EncodeContext *s = avctx->priv_data;
> +    uint64_t mask = av_channel_layout_subset(&avctx->ch_layout, ~(uint64_t)0);

Might as well use UINT64_MAX.

>       int channels = avctx->ch_layout.nb_channels;
> -    uint64_t mask = avctx->ch_layout.u.mask;
>   
>       if (channels < 1 || channels > AC3_MAX_CHANNELS)
>           return AVERROR(EINVAL);
>       if (mask > 0x7FF)
>           return AVERROR(EINVAL);
>   
> -    if (!mask)
> -        av_channel_layout_default(&avctx->ch_layout, channels);
> -    mask = avctx->ch_layout.u.mask;
> -
>       s->lfe_on       = !!(mask & AV_CH_LOW_FREQUENCY);
>       s->channels     = channels;
>       s->fbw_channels = channels - s->lfe_on;
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