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

[Paul B Mahol <onemda@gmail.com>]

On 10/30/22, James Almer <jamrial@gmail.com> wrote:
> On 10/30/2022 3:58 PM, Paul B Mahol wrote:
>> On 10/30/22, James Almer <jamrial@gmail.com> wrote:
>>> On 10/30/2022 3:29 PM, Paul B Mahol wrote:
>>>> On 10/30/22, James Almer <jamrial@gmail.com> wrote:
>>>>>
>>>>>
>>>>> 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).
>>>>
>>>> https://en.wikipedia.org/wiki/Ambisonic_reproduction_systems#Cube
>>>
>>> "If all speakers are placed in room corners", So a 7.1 layout, besides
>>> defining one channel as LFE, is also not ideal given that it defines two
>>> speaker positions in places other than the room corners, and by no means
>>> describes a 3D cube since all speakers are at the same height.
>>> The TOP channel ids let you assign four channels to speakers placed in
>>> the top room corners.
>>
>> 7.1 is there just because it have 8 channels. No other reasons.
>
> If you want to just say "there are eight channels", then make the
> AVChannelLayout define 8 channels of order UNSPEC. Let the user then
> figure out what to do with them. But if you want to actually give each
> channel a position, then you need to use the proper IDs to describe the
> intended layout.
>
> Using 7.1 here is lying to the user, as it's telling them he needs to
> place two speakers at the front, two at the back, two to the sides, and
> all at the same height, plus one channel wrongly feeding the sub woofer.
> Not to mention what would happen if you try to downmix the stream. swr
> would just generate awful results.
> Meanwhile, using cube you'll tell the user to place one speaker on every
> corner in the room, or a downmixer how to properly handle the channels
> to get good results (e.g. on headphones).

I never claimed it is perfect solution.

Is there a way to let it use unspec but still not confuse swr to abort
and do pointless messages?
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