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https://github.com/RGBCube/serenity
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LibAudio: Mix multi-channel files more properly
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
Linus Groh
parent
fc70d88367
commit
8258618caf
2 changed files with 120 additions and 24 deletions
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@ -441,14 +441,20 @@ LoaderSamples FlacLoaderPlugin::next_frame()
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};
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u8 subframe_count = frame_channel_type_to_channel_count(channel_type);
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Vector<Vector<i64>> current_subframes;
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Vector<FixedArray<float>> current_subframes;
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current_subframes.ensure_capacity(subframe_count);
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float sample_rescale = 1 / static_cast<float>(1 << (m_current_frame->bit_depth - 1));
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dbgln_if(AFLACLOADER_DEBUG, "Samples will be rescaled from {} bits: factor {:.8f}", m_current_frame->bit_depth, sample_rescale);
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for (u8 i = 0; i < subframe_count; ++i) {
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FlacSubframeHeader new_subframe = TRY(next_subframe_header(bit_stream, i));
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Vector<i64> subframe_samples = TRY(parse_subframe(new_subframe, bit_stream));
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VERIFY(subframe_samples.size() == m_current_frame->sample_count);
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current_subframes.unchecked_append(move(subframe_samples));
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FixedArray<float> scaled_samples = TRY(FixedArray<float>::create(m_current_frame->sample_count));
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for (size_t i = 0; i < m_current_frame->sample_count; ++i)
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scaled_samples[i] = static_cast<float>(subframe_samples[i]) * sample_rescale;
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current_subframes.unchecked_append(move(scaled_samples));
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}
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// 11.2. Overview ("The audio data is composed of...")
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@ -459,55 +465,58 @@ LoaderSamples FlacLoaderPlugin::next_frame()
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[[maybe_unused]] u16 footer_checksum = TRY(bit_stream.read_bits<u16>(16));
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dbgln_if(AFLACLOADER_DEBUG, "Subframe footer checksum: {}", footer_checksum);
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float sample_rescale = 1 / static_cast<float>(1 << (m_current_frame->bit_depth - 1));
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dbgln_if(AFLACLOADER_DEBUG, "Sample rescaled from {} bits: factor {:.8f}", m_current_frame->bit_depth, sample_rescale);
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FixedArray<Sample> samples = TRY(FixedArray<Sample>::create(m_current_frame->sample_count));
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FixedArray<Sample> samples;
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switch (channel_type) {
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case FlacFrameChannelType::Mono:
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for (size_t i = 0; i < m_current_frame->sample_count; ++i)
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samples[i] = Sample { static_cast<float>(current_subframes[0][i]) * sample_rescale };
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break;
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case FlacFrameChannelType::Stereo:
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// TODO mix together surround channels on each side?
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case FlacFrameChannelType::StereoCenter:
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case FlacFrameChannelType::Surround4p0:
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case FlacFrameChannelType::Surround5p0:
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case FlacFrameChannelType::Surround5p1:
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case FlacFrameChannelType::Surround6p1:
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case FlacFrameChannelType::Surround7p1:
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for (size_t i = 0; i < m_current_frame->sample_count; ++i)
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samples[i] = { static_cast<float>(current_subframes[0][i]) * sample_rescale, static_cast<float>(current_subframes[1][i]) * sample_rescale };
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case FlacFrameChannelType::Surround7p1: {
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auto new_samples = TRY(downmix_surround_to_stereo<FixedArray<float>>(move(current_subframes)));
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samples.swap(new_samples);
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break;
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case FlacFrameChannelType::LeftSideStereo:
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}
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case FlacFrameChannelType::LeftSideStereo: {
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auto new_samples = TRY(FixedArray<Sample>::create(m_current_frame->sample_count));
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samples.swap(new_samples);
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// channels are left (0) and side (1)
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for (size_t i = 0; i < m_current_frame->sample_count; ++i) {
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// right = left - side
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samples[i] = { static_cast<float>(current_subframes[0][i]) * sample_rescale,
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static_cast<float>(current_subframes[0][i] - current_subframes[1][i]) * sample_rescale };
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samples[i] = { current_subframes[0][i],
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current_subframes[0][i] - current_subframes[1][i] };
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}
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break;
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case FlacFrameChannelType::RightSideStereo:
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}
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case FlacFrameChannelType::RightSideStereo: {
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auto new_samples = TRY(FixedArray<Sample>::create(m_current_frame->sample_count));
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samples.swap(new_samples);
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// channels are side (0) and right (1)
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for (size_t i = 0; i < m_current_frame->sample_count; ++i) {
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// left = right + side
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samples[i] = { static_cast<float>(current_subframes[1][i] + current_subframes[0][i]) * sample_rescale,
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static_cast<float>(current_subframes[1][i]) * sample_rescale };
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samples[i] = { current_subframes[1][i] + current_subframes[0][i],
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current_subframes[1][i] };
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}
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break;
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case FlacFrameChannelType::MidSideStereo:
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}
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case FlacFrameChannelType::MidSideStereo: {
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auto new_samples = TRY(FixedArray<Sample>::create(m_current_frame->sample_count));
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samples.swap(new_samples);
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// channels are mid (0) and side (1)
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for (size_t i = 0; i < current_subframes[0].size(); ++i) {
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i64 mid = current_subframes[0][i];
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i64 side = current_subframes[1][i];
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float mid = current_subframes[0][i];
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float side = current_subframes[1][i];
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mid *= 2;
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// prevent integer division errors
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samples[i] = { (static_cast<float>(mid + side) * .5f) * sample_rescale,
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(static_cast<float>(mid - side) * .5f) * sample_rescale };
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samples[i] = { (mid + side) * .5f,
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(mid - side) * .5f };
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}
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break;
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}
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}
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return samples;
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#undef FLAC_VERIFY
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87
Userland/Libraries/LibAudio/MultiChannel.h
Normal file
87
Userland/Libraries/LibAudio/MultiChannel.h
Normal file
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@ -0,0 +1,87 @@
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/*
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* Copyright (c) 2023, kleines Filmröllchen <filmroellchen@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Concepts.h>
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#include <AK/FixedArray.h>
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#include <LibAudio/Sample.h>
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namespace Audio {
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// Downmixes any number of channels to stereo, under the assumption that standard channel layout is followed:
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// 1 channel = mono
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// 2 channels = stereo (left, right)
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// 3 channels = left, right, center
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// 4 channels = front left/right, back left/right
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// 5 channels = front left/right, center, back left/right
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// 6 channels = front left/right, center, LFE, back left/right
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// 7 channels = front left/right, center, LFE, back center, side left/right
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// 8 channels = front left/right, center, LFE, back left/right, side left/right
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template<ArrayLike<float> ChannelType, ArrayLike<ChannelType> InputType>
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ErrorOr<FixedArray<Sample>> downmix_surround_to_stereo(InputType input)
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{
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if (input.size() == 0)
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return Error::from_string_view("Cannot resample from 0 channels"sv);
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auto channel_count = input.size();
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auto sample_count = input[0].size();
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FixedArray<Sample> output = TRY(FixedArray<Sample>::create(sample_count));
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// FIXME: We could figure out a better way to mix the channels, possibly spatially, but for now:
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// - Center and LFE channels are added to both left and right.
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// - All left channels are added together on the left, all right channels are added together on the right.
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switch (channel_count) {
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case 1:
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for (auto i = 0u; i < sample_count; ++i)
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output[i] = Sample { input[0][i] };
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break;
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case 2:
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for (auto i = 0u; i < sample_count; ++i)
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output[i] = Sample { input[0][i], input[1][i] };
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break;
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case 3:
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for (auto i = 0u; i < sample_count; ++i)
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output[i] = Sample { input[0][i] + input[2][i],
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input[1][i] + input[2][i] };
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break;
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case 4:
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for (auto i = 0u; i < sample_count; ++i)
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output[i] = Sample { input[0][i] + input[2][i],
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input[1][i] + input[3][i] };
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break;
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case 5:
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for (auto i = 0u; i < sample_count; ++i)
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output[i] = Sample { input[0][i] + input[3][i] + input[2][i],
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input[1][i] + input[4][i] + input[2][i] };
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break;
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case 6:
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for (auto i = 0u; i < sample_count; ++i) {
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output[i] = Sample { input[0][i] + input[4][i] + input[2][i] + input[3][i],
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input[1][i] + input[5][i] + input[2][i] + input[3][i] };
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}
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break;
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case 7:
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for (auto i = 0u; i < sample_count; ++i) {
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output[i] = Sample { input[0][i] + input[5][i] + input[2][i] + input[3][i] + input[4][i],
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input[1][i] + input[6][i] + input[2][i] + input[3][i] + input[4][i] };
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}
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break;
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case 8:
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for (auto i = 0u; i < sample_count; ++i) {
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output[i] = Sample { input[0][i] + input[4][i] + input[6][i] + input[2][i] + input[3][i],
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input[1][i] + input[5][i] + input[7][i] + input[2][i] + input[3][i] };
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}
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break;
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default:
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return Error::from_string_view("Invalid number of channels greater than 8"sv);
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}
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return output;
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}
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}
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