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LibAudio: Mix multi-channel files more properly

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We downsample multi-channel files into stereo for now, which at least
makes the other channels listenable. The new multi-channel downmix
helper is intended to be used for other formats with the same or similar
channel arrangement, such as QOA.
This commit is contained in:
kleines Filmröllchen 2023-06-27 23:28:51 +02:00 • committed by Linus Groh
parent fc70d88367
commit 8258618caf
2 changed files with 120 additions and 24 deletions
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87
Userland/Libraries/LibAudio/MultiChannel.h Normal file
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/*
* Copyright (c) 2023, kleines Filmröllchen <filmroellchen@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Concepts.h>
#include <AK/FixedArray.h>
#include <LibAudio/Sample.h>
namespace Audio {
// Downmixes any number of channels to stereo, under the assumption that standard channel layout is followed:
// 1 channel = mono
// 2 channels = stereo (left, right)
// 3 channels = left, right, center
// 4 channels = front left/right, back left/right
// 5 channels = front left/right, center, back left/right
// 6 channels = front left/right, center, LFE, back left/right
// 7 channels = front left/right, center, LFE, back center, side left/right
// 8 channels = front left/right, center, LFE, back left/right, side left/right
template<ArrayLike<float> ChannelType, ArrayLike<ChannelType> InputType>
ErrorOr<FixedArray<Sample>> downmix_surround_to_stereo(InputType input)
{
if (input.size() == 0)
return Error::from_string_view("Cannot resample from 0 channels"sv);
auto channel_count = input.size();
auto sample_count = input[0].size();
FixedArray<Sample> output = TRY(FixedArray<Sample>::create(sample_count));
// FIXME: We could figure out a better way to mix the channels, possibly spatially, but for now:
// - Center and LFE channels are added to both left and right.
// - All left channels are added together on the left, all right channels are added together on the right.
switch (channel_count) {
case 1:
for (auto i = 0u; i < sample_count; ++i)
output[i] = Sample { input[0][i] };
break;
case 2:
for (auto i = 0u; i < sample_count; ++i)
output[i] = Sample { input[0][i], input[1][i] };
break;
case 3:
for (auto i = 0u; i < sample_count; ++i)
output[i] = Sample { input[0][i] + input[2][i],
input[1][i] + input[2][i] };
break;
case 4:
for (auto i = 0u; i < sample_count; ++i)
output[i] = Sample { input[0][i] + input[2][i],
input[1][i] + input[3][i] };
break;
case 5:
for (auto i = 0u; i < sample_count; ++i)
output[i] = Sample { input[0][i] + input[3][i] + input[2][i],
input[1][i] + input[4][i] + input[2][i] };
break;
case 6:
for (auto i = 0u; i < sample_count; ++i) {
output[i] = Sample { input[0][i] + input[4][i] + input[2][i] + input[3][i],
input[1][i] + input[5][i] + input[2][i] + input[3][i] };
}
break;
case 7:
for (auto i = 0u; i < sample_count; ++i) {
output[i] = Sample { input[0][i] + input[5][i] + input[2][i] + input[3][i] + input[4][i],
input[1][i] + input[6][i] + input[2][i] + input[3][i] + input[4][i] };
}
break;
case 8:
for (auto i = 0u; i < sample_count; ++i) {
output[i] = Sample { input[0][i] + input[4][i] + input[6][i] + input[2][i] + input[3][i],
input[1][i] + input[5][i] + input[7][i] + input[2][i] + input[3][i] };
}
break;
default:
return Error::from_string_view("Invalid number of channels greater than 8"sv);
}
return output;
}
}