gecko-dev/content/media/AudioChannelFormat.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/. */

#include "AudioChannelFormat.h"
#include "nsTArray.h"

#include <algorithm>

namespace mozilla {

enum {
  SURROUND_L,
  SURROUND_R,
  SURROUND_C,
  SURROUND_LFE,
  SURROUND_SL,
  SURROUND_SR
};

static const uint32_t CUSTOM_CHANNEL_LAYOUTS = 6;

static const int IGNORE = CUSTOM_CHANNEL_LAYOUTS;
static const float IGNORE_F = 0.0f;

uint32_t
GetAudioChannelsSuperset(uint32_t aChannels1, uint32_t aChannels2)
{
  return std::max(aChannels1, aChannels2);
}

/**
 * UpMixMatrix represents a conversion matrix by exploiting the fact that
 * each output channel comes from at most one input channel.
 */
struct UpMixMatrix {
  uint8_t mInputDestination[CUSTOM_CHANNEL_LAYOUTS];
};

static const UpMixMatrix
gUpMixMatrices[CUSTOM_CHANNEL_LAYOUTS*(CUSTOM_CHANNEL_LAYOUTS - 1)/2] =
{
  // Upmixes from mono
  { { 0, 0 } },
  { { 0, IGNORE, IGNORE } },
  { { 0, 0, IGNORE, IGNORE } },
  { { 0, IGNORE, IGNORE, IGNORE, IGNORE } },
  { { IGNORE, IGNORE, 0, IGNORE, IGNORE, IGNORE } },
  // Upmixes from stereo
  { { 0, 1, IGNORE } },
  { { 0, 1, IGNORE, IGNORE } },
  { { 0, 1, IGNORE, IGNORE, IGNORE } },
  { { 0, 1, IGNORE, IGNORE, IGNORE, IGNORE } },
  // Upmixes from 3-channel
  { { 0, 1, 2, IGNORE } },
  { { 0, 1, 2, IGNORE, IGNORE } },
  { { 0, 1, 2, IGNORE, IGNORE, IGNORE } },
  // Upmixes from quad
  { { 0, 1, 2, 3, IGNORE } },
  { { 0, 1, IGNORE, IGNORE, 2, 3 } },
  // Upmixes from 5-channel
  { { 0, 1, 2, 3, 4, IGNORE } }
};

static const int gMixingMatrixIndexByChannels[CUSTOM_CHANNEL_LAYOUTS - 1] =
  { 0, 5, 9, 12, 14 };

void
AudioChannelsUpMix(nsTArray<const void*>* aChannelArray,
                   uint32_t aOutputChannelCount,
                   const void* aZeroChannel)
{
  uint32_t inputChannelCount = aChannelArray->Length();
  uint32_t outputChannelCount =
    GetAudioChannelsSuperset(aOutputChannelCount, inputChannelCount);
  NS_ASSERTION(outputChannelCount > inputChannelCount,
               "No up-mix needed");
  NS_ASSERTION(inputChannelCount > 0, "Bad number of channels");
  NS_ASSERTION(outputChannelCount > 0, "Bad number of channels");

  aChannelArray->SetLength(outputChannelCount);

  if (inputChannelCount < CUSTOM_CHANNEL_LAYOUTS &&
      outputChannelCount <= CUSTOM_CHANNEL_LAYOUTS) {
    const UpMixMatrix& m = gUpMixMatrices[
      gMixingMatrixIndexByChannels[inputChannelCount - 1] +
      outputChannelCount - inputChannelCount - 1];

    const void* outputChannels[CUSTOM_CHANNEL_LAYOUTS];

    for (uint32_t i = 0; i < outputChannelCount; ++i) {
      uint8_t channelIndex = m.mInputDestination[i];
      if (channelIndex == IGNORE) {
        outputChannels[i] = aZeroChannel;
      } else {
        outputChannels[i] = aChannelArray->ElementAt(channelIndex);
      }
    }
    for (uint32_t i = 0; i < outputChannelCount; ++i) {
      aChannelArray->ElementAt(i) = outputChannels[i];
    }
    return;
  }

  for (uint32_t i = inputChannelCount; i < outputChannelCount; ++i) {
    aChannelArray->ElementAt(i) = 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 } }
};

void
AudioChannelsDownMix(const nsTArray<const void*>& aChannelArray,
                     float** 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(float));
    }
    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
    float outputChannels[CUSTOM_CHANNEL_LAYOUTS + 1];
    memset(outputChannels, 0, sizeof(float)*(CUSTOM_CHANNEL_LAYOUTS));
    for (uint32_t c = 0; c < inputChannelCount; ++c) {
      outputChannels[m.mInputDestination[c]] +=
        m.mInputCoefficient[c]*(static_cast<const float*>(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 float*>(inputChannels[SURROUND_C]))[s];
    }

    for (uint32_t c = 0; c < aOutputChannelCount; ++c) {
      aOutputChannels[c][s] = outputChannels[c];
    }
  }
}

}