gecko-dev/dom/media/AudioChannelFormat.h

178 lines
6.4 KiB
C++

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef MOZILLA_AUDIOCHANNELFORMAT_H_
#define MOZILLA_AUDIOCHANNELFORMAT_H_
#include <stdint.h>
#include "nsTArrayForwardDeclare.h"
#include "AudioSampleFormat.h"
#include "nsTArray.h"
namespace mozilla {
/*
* This file provides utilities for upmixing and downmixing channels.
*
* The channel layouts, upmixing and downmixing are consistent with the
* Web Audio spec.
*
* Channel layouts for up to 6 channels:
* mono { M }
* stereo { L, R }
* { L, R, C }
* quad { L, R, SL, SR }
* { L, R, C, SL, SR }
* 5.1 { L, R, C, LFE, SL, SR }
*
* Only 1, 2, 4 and 6 are currently defined in Web Audio.
*/
enum {
SURROUND_L,
SURROUND_R,
SURROUND_C,
SURROUND_LFE,
SURROUND_SL,
SURROUND_SR
};
const uint32_t CUSTOM_CHANNEL_LAYOUTS = 6;
// This is defined by some Windows SDK header.
#undef IGNORE
const int IGNORE = CUSTOM_CHANNEL_LAYOUTS;
const float IGNORE_F = 0.0f;
const int gMixingMatrixIndexByChannels[CUSTOM_CHANNEL_LAYOUTS - 1] =
{ 0, 5, 9, 12, 14 };
/**
* Return a channel count whose channel layout includes all the channels from
* aChannels1 and aChannels2.
*/
uint32_t
GetAudioChannelsSuperset(uint32_t aChannels1, uint32_t aChannels2);
/**
* Given an array of input channel data, and an output channel count,
* replaces the array with an array of upmixed channels.
* This shuffles the array and may set some channel buffers to aZeroChannel.
* Don't call this with input count >= output count.
* This may return *more* channels than requested. In that case, downmixing
* is required to to get to aOutputChannelCount. (This is how we handle
* odd cases like 3 -> 4 upmixing.)
* If aChannelArray.Length() was the input to one of a series of
* GetAudioChannelsSuperset calls resulting in aOutputChannelCount,
* no downmixing will be required.
*/
void
AudioChannelsUpMix(nsTArray<const void*>* aChannelArray,
uint32_t aOutputChannelCount,
const void* aZeroChannel);
/**
* DownMixMatrix represents a conversion matrix efficiently by exploiting the
* fact that each input channel contributes to at most one output channel,
* except possibly for the C input channel in layouts that have one. Also,
* every input channel is multiplied by the same coefficient for every output
* channel it contributes to.
*/
struct DownMixMatrix {
// Every input channel c is copied to output channel mInputDestination[c]
// after multiplying by mInputCoefficient[c].
uint8_t mInputDestination[CUSTOM_CHANNEL_LAYOUTS];
// If not IGNORE, then the C channel is copied to this output channel after
// multiplying by its coefficient.
uint8_t mCExtraDestination;
float mInputCoefficient[CUSTOM_CHANNEL_LAYOUTS];
};
static const DownMixMatrix
gDownMixMatrices[CUSTOM_CHANNEL_LAYOUTS*(CUSTOM_CHANNEL_LAYOUTS - 1)/2] =
{
// Downmixes to mono
{ { 0, 0 }, IGNORE, { 0.5f, 0.5f } },
{ { 0, IGNORE, IGNORE }, IGNORE, { 1.0f, IGNORE_F, IGNORE_F } },
{ { 0, 0, 0, 0 }, IGNORE, { 0.25f, 0.25f, 0.25f, 0.25f } },
{ { 0, IGNORE, IGNORE, IGNORE, IGNORE }, IGNORE, { 1.0f, IGNORE_F, IGNORE_F, IGNORE_F, IGNORE_F } },
{ { 0, 0, 0, IGNORE, 0, 0 }, IGNORE, { 0.7071f, 0.7071f, 1.0f, IGNORE_F, 0.5f, 0.5f } },
// Downmixes to stereo
{ { 0, 1, IGNORE }, IGNORE, { 1.0f, 1.0f, IGNORE_F } },
{ { 0, 1, 0, 1 }, IGNORE, { 0.5f, 0.5f, 0.5f, 0.5f } },
{ { 0, 1, IGNORE, IGNORE, IGNORE }, IGNORE, { 1.0f, 1.0f, IGNORE_F, IGNORE_F, IGNORE_F } },
{ { 0, 1, 0, IGNORE, 0, 1 }, 1, { 1.0f, 1.0f, 0.7071f, IGNORE_F, 0.7071f, 0.7071f } },
// Downmixes to 3-channel
{ { 0, 1, 2, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, IGNORE_F } },
{ { 0, 1, 2, IGNORE, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, IGNORE_F, IGNORE_F } },
{ { 0, 1, 2, IGNORE, IGNORE, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, IGNORE_F, IGNORE_F, IGNORE_F } },
// Downmixes to quad
{ { 0, 1, 2, 3, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, 1.0f, IGNORE_F } },
{ { 0, 1, 0, IGNORE, 2, 3 }, 1, { 1.0f, 1.0f, 0.7071f, IGNORE_F, 1.0f, 1.0f } },
// Downmixes to 5-channel
{ { 0, 1, 2, 3, 4, IGNORE }, IGNORE, { 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, IGNORE_F } }
};
/**
* Given an array of input channels, downmix to aOutputChannelCount, and copy
* the results to the channel buffers in aOutputChannels. Don't call this with
* input count <= output count.
*/
template<typename T>
void AudioChannelsDownMix(const nsTArray<const void*>& aChannelArray,
T** aOutputChannels,
uint32_t aOutputChannelCount,
uint32_t aDuration)
{
uint32_t inputChannelCount = aChannelArray.Length();
const void* const* inputChannels = aChannelArray.Elements();
NS_ASSERTION(inputChannelCount > aOutputChannelCount, "Nothing to do");
if (inputChannelCount > 6) {
// Just drop the unknown channels.
for (uint32_t o = 0; o < aOutputChannelCount; ++o) {
memcpy(aOutputChannels[o], inputChannels[o], aDuration*sizeof(T));
}
return;
}
// Ignore unknown channels, they're just dropped.
inputChannelCount = std::min<uint32_t>(6, inputChannelCount);
const DownMixMatrix& m = gDownMixMatrices[
gMixingMatrixIndexByChannels[aOutputChannelCount - 1] +
inputChannelCount - aOutputChannelCount - 1];
// This is slow, but general. We can define custom code for special
// cases later.
for (uint32_t s = 0; s < aDuration; ++s) {
// Reserve an extra junk channel at the end for the cases where we
// want an input channel to contribute to nothing
T outputChannels[CUSTOM_CHANNEL_LAYOUTS + 1];
memset(outputChannels, 0, sizeof(T)*(CUSTOM_CHANNEL_LAYOUTS));
for (uint32_t c = 0; c < inputChannelCount; ++c) {
outputChannels[m.mInputDestination[c]] +=
m.mInputCoefficient[c]*(static_cast<const T*>(inputChannels[c]))[s];
}
// Utilize the fact that in every layout, C is the third channel.
if (m.mCExtraDestination != IGNORE) {
outputChannels[m.mCExtraDestination] +=
m.mInputCoefficient[SURROUND_C]*(static_cast<const T*>(inputChannels[SURROUND_C]))[s];
}
for (uint32_t c = 0; c < aOutputChannelCount; ++c) {
aOutputChannels[c][s] = outputChannels[c];
}
}
}
} // namespace mozilla
#endif /* MOZILLA_AUDIOCHANNELFORMAT_H_ */