Re: [FFmpeg-devel] [PATCH] avfilter: add ambisonic decoder filter

[James Almer <jamrial@gmail.com>]

On 10/30/2022 3:19 PM, Paul B Mahol wrote:
> On 10/30/22, James Almer <jamrial@gmail.com> wrote:
>> On 10/30/2022 12:34 PM, Paul B Mahol wrote:
>>> +static const struct {
>>> +    const int              order;
>>> +    const int              inputs;
>>> +    const int              speakers;
>>> +    const int              near_field;
>>> +    const int              type;
>>> +    const double           xover;
>>> +    const AVChannelLayout  outlayout;
>>> +    const double          *speakers_azimuth;
>>> +    const double          *speakers_elevation;
>>> +    const double          *speakers_distance;
>>> +} ambisonic_tab[] = {
>>> +    [MONO] = {
>>> +        .order = 0,
>>> +        .inputs = 1,
>>> +        .speakers = 1,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_MONO,
>>> +        .speakers_azimuth = (const double[1]){ 0. },
>>> +        .speakers_distance = (const double[1]){ 1. },
>>> +    },
>>> +    [STEREO] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 2,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_STEREO,
>>> +        .speakers_azimuth = (const double[2]){ -30, 30},
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [STEREO_DOWNMIX] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 2,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_STEREO_DOWNMIX,
>>> +        .speakers_azimuth = (const double[2]){ -90, 90 },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [SURROUND] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 3,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_SURROUND,
>>> +        .speakers_azimuth = (const double[3]){ -45, 45, 0 },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [L2_1] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 3,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_2_1,
>>> +        .speakers_azimuth = (const double[3]){ -45, 45, 180 },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [TRIANGLE] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 3,
>>> +        .type = 1,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_SURROUND,
>>> +        .speakers_azimuth = (const double[3]){ -120, 120, 0 },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [QUAD] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 4,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_QUAD,
>>> +        .speakers_azimuth = (const double[4]){ -45, 45, -135, 135 },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [SQUARE] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 4,
>>> +        .type = 1,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_4POINT0,
>>> +        .speakers_azimuth = (const double[4]){ 0, -90, 180, 90 },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [L4_0] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 4,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_4POINT0,
>>> +        .speakers_azimuth = (const double[4]){ -30, 30, 0, 180 },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [L5_0] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 5,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_5POINT0_BACK,
>>> +        .speakers_azimuth = (const double[5]){ -30, 30, 0, -145, 145 },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [L5_0_SIDE] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 5,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_5POINT0,
>>> +        .speakers_azimuth = (const double[5]){ -30, 30, 0, -110, 110 },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [L6_0] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 6,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_6POINT0,
>>> +        .speakers_azimuth = (const double[6]){ -30, 30, 0, 180, -110, 110
>>> },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [L7_0] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 7,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_7POINT0,
>>> +        .speakers_azimuth = (const double[7]){ -30, 30, 0, -145, 145,
>>> -110, 110 },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [TETRA] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 4,
>>> +        .type = 2,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_QUAD,
>>> +        .speakers_azimuth = (const double[4]){ -90, 90, 0, 180 },
>>> +        .speakers_elevation = (const double[4]){ -35.3, -35.3, 35.3, 35.3
>>> },
>>> +        .speakers_distance = same_distance,
>>> +    },
>>> +    [CUBE] = {
>>> +        .order = 1,
>>> +        .inputs = 4,
>>> +        .speakers = 8,
>>> +        .type = 2,
>>> +        .near_field = NF_NONE,
>>> +        .xover = 0.,
>>> +        .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_7POINT1,
>>
>> 7.1 defines an LFE channel, which is clearly not intended here, so it
>> should be either:
>>
>> .outlayout = (AVChannelLayout)AV_CHANNEL_LAYOUT_MASK(8,
>>                    AV_CH_LAYOUT_QUAD     |
>>                    AV_CH_TOP_FRONT_LEFT  |
>>                    AV_CH_TOP_FRONT_RIGHT |
>>                    AV_CH_TOP_BACK_LEFT   |
>>                    AV_CH_TOP_BACK_RIGHT),
>>
>> Or the AV_CHANNEL_LAYOUT_CUBE layout (using the exact same bitmask as
>> above) after the patch i sent just now is committed.
> 
> CUBE is as real cube in 3d space. No current layout in API can be
> described correctly.

the TOP_* channels are in a different height layer than the other 
channels, namely above them. The result for this bitmask is a 3D cube 
layout (Left and right speakers both front and back, in two different 
height layers).

> 
>>
>>> +        .speakers_azimuth = cube_azimuth,
>>> +        .speakers_elevation = cube_elevation,
>>> +        .speakers_distance = same_distance,
>>> +    },
>>
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