Re: [FFmpeg-devel] [PATCH v2 2/4] avutil/channel_layout: factorize ambisonic order detection

[Marton Balint <cus@passwd.hu>]

On Tue, 15 Mar 2022, James Almer wrote:

>
>
> On 3/15/2022 6:18 PM, Marton Balint wrote:
>>  Signed-off-by: Marton Balint <cus@passwd.hu>
>>  ---
>>    libavutil/channel_layout.c | 42 +++++++++++++++++++++++++++-----------
>>    libavutil/channel_layout.h |  1 +
>>    2 files changed, 31 insertions(+), 12 deletions(-)
>>
>>  diff --git a/libavutil/channel_layout.c b/libavutil/channel_layout.c
>>  index c60ccf368f..0069c6257b 100644
>>  --- a/libavutil/channel_layout.c
>>  +++ b/libavutil/channel_layout.c
>>  @@ -644,29 +644,31 @@ int av_channel_layout_copy(AVChannelLayout *dst,
>>  const AVChannelLayout *src)
>>    }
>>
>>    /**
>>  - * 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.
>>  + * If the layout is n-th order standard-order ambisonic, with optional
>>  + * extra non-diegetic channels at the end, return the order.
>>  + * Return a negative error code otherwise.
>>     */
>>  -static int try_describe_ambisonic(AVBPrint *bp, const AVChannelLayout
>>  *channel_layout)
>>  +static int ambisonic_order(const AVChannelLayout *channel_layout)
>>    {
>>        int i, highest_ambi, order;
>>
>>        highest_ambi = -1;
>>  -    if (channel_layout->order == AV_CHANNEL_ORDER_AMBISONIC)
>>  +    if (channel_layout->order == AV_CHANNEL_ORDER_AMBISONIC) {
>>            highest_ambi = channel_layout->nb_channels -
>>  av_popcount64(channel_layout->u.mask) - 1;
>>  -    else {
>>  +    } else {
>
> nit: Remove these brackets since it's still a single line after the if 
> statement. They bloat the diff for no gain.

Ok.

>
>>            const AVChannelCustom *map = channel_layout->u.map;
>>  +        av_assert0(channel_layout->order == AV_CHANNEL_ORDER_CUSTOM);
>>  +
>>            for (i = 0; i < channel_layout->nb_channels; i++) {
>>                int is_ambi = CHAN_IS_AMBI(map[i].id);
>>
>>                /* ambisonic following non-ambisonic */
>>                if (i > 0 && is_ambi && !CHAN_IS_AMBI(map[i - 1].id))
>>  -                return 0;
>>  +                return AVERROR(EINVAL);
>>
>>                /* non-default ordering */
>>                if (is_ambi && map[i].id - AV_CHAN_AMBISONIC_BASE != i)
>>  -                return 0;
>>  +                return AVERROR(EINVAL);
>>
>>                if (CHAN_IS_AMBI(map[i].id))
>>                    highest_ambi = i;
>>  @@ -674,17 +676,33 @@ static int try_describe_ambisonic(AVBPrint *bp,
>>  const AVChannelLayout *channel_l
>>        }
>>        /* no ambisonic channels*/
>>        if (highest_ambi < 0)
>>  -        return 0;
>>  +        return AVERROR(EINVAL);
>>
>>        order = floor(sqrt(highest_ambi));
>>        /* incomplete order - some harmonics are missing */
>>        if ((order + 1) * (order + 1) != highest_ambi + 1)
>>  +        return AVERROR(EINVAL);
>>  +
>>  +    return order;
>>  +}
>>  +
>>  +/**
>>  + * 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.
>>  + */
>>  +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;
>>
>>        av_bprintf(bp, "ambisonic %d", order);
>>
>>        /* extra channels present */
>>  -    if (highest_ambi < channel_layout->nb_channels - 1) {
>>  +    nb_ambi_channels = (order + 1) * (order + 1);
>>  +    if (nb_ambi_channels < channel_layout->nb_channels) {
>>            AVChannelLayout extra = { 0 };
>>            char buf[128];
>>    @@ -696,12 +714,12 @@ static int try_describe_ambisonic(AVBPrint *bp,
>>  const AVChannelLayout *channel_l
>>                const AVChannelCustom *map = channel_layout->u.map;
>>
>>                extra.order       = AV_CHANNEL_ORDER_CUSTOM;
>>  -            extra.nb_channels = channel_layout->nb_channels -
>>  highest_ambi - 1;
>>  +            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[highest_ambi + 1],
>>  +            memcpy(extra.u.map, &map[nb_ambi_channels],
>>                       sizeof(*extra.u.map) * extra.nb_channels);
>>            }
>>    diff --git a/libavutil/channel_layout.h b/libavutil/channel_layout.h
>>  index 4dd6614de9..294e8b0773 100644
>>  --- a/libavutil/channel_layout.h
>>  +++ b/libavutil/channel_layout.h
>>  @@ -27,6 +27,7 @@
>>
>>    #include "version.h"
>>    #include "attributes.h"
>>  +#include "avassert.h"
>
> Nothing in the header uses it. It'll become an unnecessary dependency every 
> user of this header will have to deal with, so add it to channel_layout.c 
> instead.

Ok, I have no idea why I added it to the header... :)

Thanks,
Marton
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