249 lines
8.7 KiB
C++
249 lines
8.7 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim:set ts=2 sw=2 sts=2 et cindent: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef MOZILLA_AUDIOCHANNELFORMAT_H_
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#define MOZILLA_AUDIOCHANNELFORMAT_H_
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#include <stdint.h>
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#include "nsTArrayForwardDeclare.h"
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#include "AudioSampleFormat.h"
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#include "nsTArray.h"
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namespace mozilla {
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/*
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* This file provides utilities for upmixing and downmixing channels.
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*
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* The channel layouts, upmixing and downmixing are consistent with the
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* Web Audio spec.
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*
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* Channel layouts for up to 6 channels:
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* mono { M }
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* stereo { L, R }
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* { L, R, C }
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* quad { L, R, SL, SR }
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* { L, R, C, SL, SR }
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* 5.1 { L, R, C, LFE, SL, SR }
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*
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* Only 1, 2, 4 and 6 are currently defined in Web Audio.
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*/
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enum {
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SURROUND_L,
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SURROUND_R,
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SURROUND_C,
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SURROUND_LFE,
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SURROUND_SL,
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SURROUND_SR
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};
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const uint32_t CUSTOM_CHANNEL_LAYOUTS = 6;
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// This is defined by some Windows SDK header.
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#undef IGNORE
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const int IGNORE = CUSTOM_CHANNEL_LAYOUTS;
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const float IGNORE_F = 0.0f;
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const int gMixingMatrixIndexByChannels[CUSTOM_CHANNEL_LAYOUTS - 1] =
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{ 0, 5, 9, 12, 14 };
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/**
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* Return a channel count whose channel layout includes all the channels from
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* aChannels1 and aChannels2.
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*/
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uint32_t
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GetAudioChannelsSuperset(uint32_t aChannels1, uint32_t aChannels2);
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/**
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* DownMixMatrix represents a conversion matrix efficiently by exploiting the
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* fact that each input channel contributes to at most one output channel,
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* except possibly for the C input channel in layouts that have one. Also,
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* every input channel is multiplied by the same coefficient for every output
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* channel it contributes to.
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*/
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const float SQRT_ONE_HALF = 0.7071067811865476f;
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struct DownMixMatrix {
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// Every input channel c is copied to output channel mInputDestination[c]
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// after multiplying by mInputCoefficient[c].
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uint8_t mInputDestination[CUSTOM_CHANNEL_LAYOUTS];
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// If not IGNORE, then the C channel is copied to this output channel after
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// multiplying by its coefficient.
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uint8_t mCExtraDestination;
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float mInputCoefficient[CUSTOM_CHANNEL_LAYOUTS];
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};
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static const DownMixMatrix
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gDownMixMatrices[CUSTOM_CHANNEL_LAYOUTS*(CUSTOM_CHANNEL_LAYOUTS - 1)/2] =
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{
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// Downmixes to mono
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{ { 0, 0 }, IGNORE, { 0.5f, 0.5f } },
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{ { 0, IGNORE, IGNORE }, IGNORE, { 1.0f, IGNORE_F, IGNORE_F } },
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{ { 0, 0, 0, 0 }, IGNORE, { 0.25f, 0.25f, 0.25f, 0.25f } },
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{ { 0, IGNORE, IGNORE, IGNORE, IGNORE }, IGNORE, { 1.0f, IGNORE_F, IGNORE_F, IGNORE_F, IGNORE_F } },
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{ { 0, 0, 0, IGNORE, 0, 0 }, IGNORE, { SQRT_ONE_HALF, SQRT_ONE_HALF, 1.0f, IGNORE_F, 0.5f, 0.5f } },
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// Downmixes to stereo
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{ { 0, 1, IGNORE }, IGNORE, { 1.0f, 1.0f, IGNORE_F } },
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{ { 0, 1, 0, 1 }, IGNORE, { 0.5f, 0.5f, 0.5f, 0.5f } },
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{ { 0, 1, IGNORE, IGNORE, IGNORE }, IGNORE, { 1.0f, 1.0f, IGNORE_F, IGNORE_F, IGNORE_F } },
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{ { 0, 1, 0, IGNORE, 0, 1 }, 1, { 1.0f, 1.0f, SQRT_ONE_HALF, IGNORE_F, SQRT_ONE_HALF, SQRT_ONE_HALF } },
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// Downmixes to 3-channel
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{ { 0, 1, 2, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, IGNORE_F } },
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{ { 0, 1, 2, IGNORE, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, IGNORE_F, IGNORE_F } },
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{ { 0, 1, 2, IGNORE, IGNORE, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, IGNORE_F, IGNORE_F, IGNORE_F } },
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// Downmixes to quad
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{ { 0, 1, 2, 3, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, 1.0f, IGNORE_F } },
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{ { 0, 1, 0, IGNORE, 2, 3 }, 1, { 1.0f, 1.0f, SQRT_ONE_HALF, IGNORE_F, 1.0f, 1.0f } },
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// Downmixes to 5-channel
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{ { 0, 1, 2, 3, 4, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, IGNORE_F } }
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};
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/**
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* Given an array of input channels, downmix to aOutputChannelCount, and copy
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* the results to the channel buffers in aOutputChannels. Don't call this with
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* input count <= output count.
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*/
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template<typename T>
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void AudioChannelsDownMix(const nsTArray<const T*>& aChannelArray,
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T** aOutputChannels,
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uint32_t aOutputChannelCount,
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uint32_t aDuration)
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{
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uint32_t inputChannelCount = aChannelArray.Length();
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const T* const* inputChannels = aChannelArray.Elements();
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NS_ASSERTION(inputChannelCount > aOutputChannelCount, "Nothing to do");
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if (inputChannelCount > 6) {
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// Just drop the unknown channels.
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for (uint32_t o = 0; o < aOutputChannelCount; ++o) {
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PodCopy(aOutputChannels[o], inputChannels[o], aDuration);
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}
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return;
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}
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// Ignore unknown channels, they're just dropped.
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inputChannelCount = std::min<uint32_t>(6, inputChannelCount);
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const DownMixMatrix& m = gDownMixMatrices[
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gMixingMatrixIndexByChannels[aOutputChannelCount - 1] +
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inputChannelCount - aOutputChannelCount - 1];
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// This is slow, but general. We can define custom code for special
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// cases later.
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for (uint32_t s = 0; s < aDuration; ++s) {
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// Reserve an extra junk channel at the end for the cases where we
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// want an input channel to contribute to nothing
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T outputChannels[CUSTOM_CHANNEL_LAYOUTS + 1] = {0};
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for (uint32_t c = 0; c < inputChannelCount; ++c) {
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outputChannels[m.mInputDestination[c]] +=
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m.mInputCoefficient[c]*(static_cast<const T*>(inputChannels[c]))[s];
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}
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// Utilize the fact that in every layout, C is the third channel.
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if (m.mCExtraDestination != IGNORE) {
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outputChannels[m.mCExtraDestination] +=
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m.mInputCoefficient[SURROUND_C]*(static_cast<const T*>(inputChannels[SURROUND_C]))[s];
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}
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for (uint32_t c = 0; c < aOutputChannelCount; ++c) {
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aOutputChannels[c][s] = outputChannels[c];
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}
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}
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}
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/**
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* UpMixMatrix represents a conversion matrix by exploiting the fact that
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* each output channel comes from at most one input channel.
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*/
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struct UpMixMatrix {
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uint8_t mInputDestination[CUSTOM_CHANNEL_LAYOUTS];
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};
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static const UpMixMatrix
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gUpMixMatrices[CUSTOM_CHANNEL_LAYOUTS*(CUSTOM_CHANNEL_LAYOUTS - 1)/2] =
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{
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// Upmixes from mono
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{ { 0, 0 } },
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{ { 0, IGNORE, IGNORE } },
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{ { 0, 0, IGNORE, IGNORE } },
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{ { 0, IGNORE, IGNORE, IGNORE, IGNORE } },
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{ { IGNORE, IGNORE, 0, IGNORE, IGNORE, IGNORE } },
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// Upmixes from stereo
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{ { 0, 1, IGNORE } },
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{ { 0, 1, IGNORE, IGNORE } },
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{ { 0, 1, IGNORE, IGNORE, IGNORE } },
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{ { 0, 1, IGNORE, IGNORE, IGNORE, IGNORE } },
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// Upmixes from 3-channel
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{ { 0, 1, 2, IGNORE } },
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{ { 0, 1, 2, IGNORE, IGNORE } },
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{ { 0, 1, 2, IGNORE, IGNORE, IGNORE } },
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// Upmixes from quad
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{ { 0, 1, 2, 3, IGNORE } },
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{ { 0, 1, IGNORE, IGNORE, 2, 3 } },
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// Upmixes from 5-channel
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{ { 0, 1, 2, 3, 4, IGNORE } }
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};
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/**
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* Given an array of input channel data, and an output channel count,
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* replaces the array with an array of upmixed channels.
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* This shuffles the array and may set some channel buffers to aZeroChannel.
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* Don't call this with input count >= output count.
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* This may return *more* channels than requested. In that case, downmixing
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* is required to to get to aOutputChannelCount. (This is how we handle
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* odd cases like 3 -> 4 upmixing.)
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* If aChannelArray.Length() was the input to one of a series of
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* GetAudioChannelsSuperset calls resulting in aOutputChannelCount,
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* no downmixing will be required.
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*/
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template<typename T>
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void
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AudioChannelsUpMix(nsTArray<const T*>* aChannelArray,
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uint32_t aOutputChannelCount,
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const T* aZeroChannel)
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{
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uint32_t inputChannelCount = aChannelArray->Length();
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uint32_t outputChannelCount =
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GetAudioChannelsSuperset(aOutputChannelCount, inputChannelCount);
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NS_ASSERTION(outputChannelCount > inputChannelCount,
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"No up-mix needed");
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MOZ_ASSERT(inputChannelCount > 0, "Bad number of channels");
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MOZ_ASSERT(outputChannelCount > 0, "Bad number of channels");
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aChannelArray->SetLength(outputChannelCount);
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if (inputChannelCount < CUSTOM_CHANNEL_LAYOUTS &&
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outputChannelCount <= CUSTOM_CHANNEL_LAYOUTS) {
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const UpMixMatrix& m = gUpMixMatrices[
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gMixingMatrixIndexByChannels[inputChannelCount - 1] +
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outputChannelCount - inputChannelCount - 1];
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const T* outputChannels[CUSTOM_CHANNEL_LAYOUTS];
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for (uint32_t i = 0; i < outputChannelCount; ++i) {
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uint8_t channelIndex = m.mInputDestination[i];
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if (channelIndex == IGNORE) {
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outputChannels[i] = aZeroChannel;
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} else {
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outputChannels[i] = aChannelArray->ElementAt(channelIndex);
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}
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}
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for (uint32_t i = 0; i < outputChannelCount; ++i) {
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aChannelArray->ElementAt(i) = outputChannels[i];
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}
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return;
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}
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for (uint32_t i = inputChannelCount; i < outputChannelCount; ++i) {
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aChannelArray->ElementAt(i) = aZeroChannel;
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}
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}
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} // namespace mozilla
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#endif /* MOZILLA_AUDIOCHANNELFORMAT_H_ */
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