media/base/channel_mixer.cc

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// MSVC++ requires this to be set before any other includes to get M_SQRT1_2.
#define _USE_MATH_DEFINES

#include "media/base/channel_mixer.h"

#include <algorithm>
#include <cmath>

#include "base/logging.h"
#include "media/audio/audio_parameters.h"
#include "media/base/audio_bus.h"
#include "media/base/vector_math.h"

namespace media {

// Default scale factor for mixing two channels together.  We use a different
// value for stereo -> mono and mono -> stereo mixes.
static const float kEqualPowerScale = static_cast<float>(M_SQRT1_2);

static void ValidateLayout(ChannelLayout layout) {
  CHECK_NE(layout, CHANNEL_LAYOUT_NONE);
  CHECK_LE(layout, CHANNEL_LAYOUT_MAX);
  CHECK_NE(layout, CHANNEL_LAYOUT_UNSUPPORTED);
  CHECK_NE(layout, CHANNEL_LAYOUT_DISCRETE);
  CHECK_NE(layout, CHANNEL_LAYOUT_STEREO_AND_KEYBOARD_MIC);

  // Verify there's at least one channel.  Should always be true here by virtue
  // of not being one of the invalid layouts, but lets double check to be sure.
  int channel_count = ChannelLayoutToChannelCount(layout);
  DCHECK_GT(channel_count, 0);

  // If we have more than one channel, verify a symmetric layout for sanity.
  // The unit test will verify all possible layouts, so this can be a DCHECK.
  // Symmetry allows simplifying the matrix building code by allowing us to
  // assume that if one channel of a pair exists, the other will too.
  if (channel_count > 1) {
    DCHECK((ChannelOrder(layout, LEFT) >= 0 &&
            ChannelOrder(layout, RIGHT) >= 0) ||
           (ChannelOrder(layout, SIDE_LEFT) >= 0 &&
            ChannelOrder(layout, SIDE_RIGHT) >= 0) ||
           (ChannelOrder(layout, BACK_LEFT) >= 0 &&
            ChannelOrder(layout, BACK_RIGHT) >= 0) ||
           (ChannelOrder(layout, LEFT_OF_CENTER) >= 0 &&
            ChannelOrder(layout, RIGHT_OF_CENTER) >= 0))
        << "Non-symmetric channel layout encountered.";
  } else {
    DCHECK_EQ(layout, CHANNEL_LAYOUT_MONO);
  }

  return;
}

class MatrixBuilder {
 public:
  MatrixBuilder(ChannelLayout input_layout, int input_channels,
                ChannelLayout output_layout, int output_channels)
      : input_layout_(input_layout),
        input_channels_(input_channels),
        output_layout_(output_layout),
        output_channels_(output_channels) {
    // Special case for 5.0, 5.1 with back channels when upmixed to 7.0, 7.1,
    // which should map the back LR to side LR.
    if (input_layout_ == CHANNEL_LAYOUT_5_0_BACK &&
        output_layout_ == CHANNEL_LAYOUT_7_0) {
      input_layout_ = CHANNEL_LAYOUT_5_0;
    } else if (input_layout_ == CHANNEL_LAYOUT_5_1_BACK &&
               output_layout_ == CHANNEL_LAYOUT_7_1) {
      input_layout_ = CHANNEL_LAYOUT_5_1;
    }
  }

  ~MatrixBuilder() { }

  // Create the transformation matrix of input channels to output channels.
  // Updates the empty matrix with the transformation, and returns true
  // if the transformation is just a remapping of channels (no mixing).
  bool CreateTransformationMatrix(std::vector< std::vector<float> >* matrix);

 private:
  // Result transformation of input channels to output channels
  std::vector< std::vector<float> >* matrix_;

  // Input and output channel layout provided during construction.
  ChannelLayout input_layout_;
  int input_channels_;
  ChannelLayout output_layout_;
  int output_channels_;

  // Helper variable for tracking which inputs are currently unaccounted,
  // should be empty after construction completes.
  std::vector<Channels> unaccounted_inputs_;

  // Helper methods for managing unaccounted input channels.
  void AccountFor(Channels ch);
  bool IsUnaccounted(Channels ch);

  // Helper methods for checking if |ch| exists in either |input_layout_| or
  // |output_layout_| respectively.
  bool HasInputChannel(Channels ch);
  bool HasOutputChannel(Channels ch);

  // Helper methods for updating |matrix_| with the proper value for
  // mixing |input_ch| into |output_ch|.  MixWithoutAccounting() does not
  // remove the channel from |unaccounted_inputs_|.
  void Mix(Channels input_ch, Channels output_ch, float scale);
  void MixWithoutAccounting(Channels input_ch, Channels output_ch,
                                          float scale);

  DISALLOW_COPY_AND_ASSIGN(MatrixBuilder);
};

ChannelMixer::ChannelMixer(ChannelLayout input_layout,
                           ChannelLayout output_layout) {
  Initialize(input_layout,
             ChannelLayoutToChannelCount(input_layout),
             output_layout,
             ChannelLayoutToChannelCount(output_layout));
}

ChannelMixer::ChannelMixer(
    const AudioParameters& input, const AudioParameters& output) {
  Initialize(input.channel_layout(),
             input.channels(),
             output.channel_layout(),
             output.channels());
}

void ChannelMixer::Initialize(
    ChannelLayout input_layout, int input_channels,
    ChannelLayout output_layout, int output_channels) {
  // Stereo down mix should never be the output layout.
  CHECK_NE(output_layout, CHANNEL_LAYOUT_STEREO_DOWNMIX);

  // Verify that the layouts are supported
  if (input_layout != CHANNEL_LAYOUT_DISCRETE)
    ValidateLayout(input_layout);
  if (output_layout != CHANNEL_LAYOUT_DISCRETE)
    ValidateLayout(output_layout);

  // Create the transformation matrix
  MatrixBuilder matrix_builder(input_layout, input_channels,
                               output_layout, output_channels);
  remapping_ = matrix_builder.CreateTransformationMatrix(&matrix_);
}

bool MatrixBuilder::CreateTransformationMatrix(
    std::vector< std::vector<float> >* matrix) {
  matrix_ = matrix;

  // Size out the initial matrix.
  matrix_->reserve(output_channels_);
  for (int output_ch = 0; output_ch < output_channels_; ++output_ch)
    matrix_->push_back(std::vector<float>(input_channels_, 0));

  // First check for discrete case.
  if (input_layout_ == CHANNEL_LAYOUT_DISCRETE ||
      output_layout_ == CHANNEL_LAYOUT_DISCRETE) {
    // If the number of input channels is more than output channels, then
    // copy as many as we can then drop the remaining input channels.
    // If the number of input channels is less than output channels, then
    // copy them all, then zero out the remaining output channels.
    int passthrough_channels = std::min(input_channels_, output_channels_);
    for (int i = 0; i < passthrough_channels; ++i)
      (*matrix_)[i][i] = 1;

    return true;
  }

  // Route matching channels and figure out which ones aren't accounted for.
  for (Channels ch = LEFT; ch < CHANNELS_MAX + 1;
       ch = static_cast<Channels>(ch + 1)) {
    int input_ch_index = ChannelOrder(input_layout_, ch);
    if (input_ch_index < 0)
      continue;

    int output_ch_index = ChannelOrder(output_layout_, ch);
    if (output_ch_index < 0) {
      unaccounted_inputs_.push_back(ch);
      continue;
    }

    DCHECK_LT(static_cast<size_t>(output_ch_index), matrix_->size());
    DCHECK_LT(static_cast<size_t>(input_ch_index),
              (*matrix_)[output_ch_index].size());
    (*matrix_)[output_ch_index][input_ch_index] = 1;
  }

  // If all input channels are accounted for, there's nothing left to do.
  if (unaccounted_inputs_.empty()) {
    // Since all output channels map directly to inputs we can optimize.
    return true;
  }

  // Mix front LR into center.
  if (IsUnaccounted(LEFT)) {
    // When down mixing to mono from stereo, we need to be careful of full scale
    // stereo mixes.  Scaling by 1 / sqrt(2) here will likely lead to clipping
    // so we use 1 / 2 instead.
    float scale =
        (output_layout_ == CHANNEL_LAYOUT_MONO && input_channels_ == 2) ?
        0.5 : kEqualPowerScale;
    Mix(LEFT, CENTER, scale);
    Mix(RIGHT, CENTER, scale);
  }

  // Mix center into front LR.
  if (IsUnaccounted(CENTER)) {
    // When up mixing from mono, just do a copy to front LR.
    float scale =
        (input_layout_ == CHANNEL_LAYOUT_MONO) ? 1 : kEqualPowerScale;
    MixWithoutAccounting(CENTER, LEFT, scale);
    Mix(CENTER, RIGHT, scale);
  }

  // Mix back LR into: side LR || back center || front LR || front center.
  if (IsUnaccounted(BACK_LEFT)) {
    if (HasOutputChannel(SIDE_LEFT)) {
      // If we have side LR, mix back LR into side LR, but instead if the input
      // doesn't have side LR (but output does) copy back LR to side LR.
      float scale = HasInputChannel(SIDE_LEFT) ? kEqualPowerScale : 1;
      Mix(BACK_LEFT, SIDE_LEFT, scale);
      Mix(BACK_RIGHT, SIDE_RIGHT, scale);
    } else if (HasOutputChannel(BACK_CENTER)) {
      // Mix back LR into back center.
      Mix(BACK_LEFT, BACK_CENTER, kEqualPowerScale);
      Mix(BACK_RIGHT, BACK_CENTER, kEqualPowerScale);
    } else if (output_layout_ > CHANNEL_LAYOUT_MONO) {
      // Mix back LR into front LR.
      Mix(BACK_LEFT, LEFT, kEqualPowerScale);
      Mix(BACK_RIGHT, RIGHT, kEqualPowerScale);
    } else {
      // Mix back LR into front center.
      Mix(BACK_LEFT, CENTER, kEqualPowerScale);
      Mix(BACK_RIGHT, CENTER, kEqualPowerScale);
    }
  }

  // Mix side LR into: back LR || back center || front LR || front center.
  if (IsUnaccounted(SIDE_LEFT)) {
    if (HasOutputChannel(BACK_LEFT)) {
      // If we have back LR, mix side LR into back LR, but instead if the input
      // doesn't have back LR (but output does) copy side LR to back LR.
      float scale = HasInputChannel(BACK_LEFT) ? kEqualPowerScale : 1;
      Mix(SIDE_LEFT, BACK_LEFT, scale);
      Mix(SIDE_RIGHT, BACK_RIGHT, scale);
    } else if (HasOutputChannel(BACK_CENTER)) {
      // Mix side LR into back center.
      Mix(SIDE_LEFT, BACK_CENTER, kEqualPowerScale);
      Mix(SIDE_RIGHT, BACK_CENTER, kEqualPowerScale);
    } else if (output_layout_ > CHANNEL_LAYOUT_MONO) {
      // Mix side LR into front LR.
      Mix(SIDE_LEFT, LEFT, kEqualPowerScale);
      Mix(SIDE_RIGHT, RIGHT, kEqualPowerScale);
    } else {
      // Mix side LR into front center.
      Mix(SIDE_LEFT, CENTER, kEqualPowerScale);
      Mix(SIDE_RIGHT, CENTER, kEqualPowerScale);
    }
  }

  // Mix back center into: back LR || side LR || front LR || front center.
  if (IsUnaccounted(BACK_CENTER)) {
    if (HasOutputChannel(BACK_LEFT)) {
      // Mix back center into back LR.
      MixWithoutAccounting(BACK_CENTER, BACK_LEFT, kEqualPowerScale);
      Mix(BACK_CENTER, BACK_RIGHT, kEqualPowerScale);
    } else if (HasOutputChannel(SIDE_LEFT)) {
      // Mix back center into side LR.
      MixWithoutAccounting(BACK_CENTER, SIDE_LEFT, kEqualPowerScale);
      Mix(BACK_CENTER, SIDE_RIGHT, kEqualPowerScale);
    } else if (output_layout_ > CHANNEL_LAYOUT_MONO) {
      // Mix back center into front LR.
      // TODO(dalecurtis): Not sure about these values?
      MixWithoutAccounting(BACK_CENTER, LEFT, kEqualPowerScale);
      Mix(BACK_CENTER, RIGHT, kEqualPowerScale);
    } else {
      // Mix back center into front center.
      // TODO(dalecurtis): Not sure about these values?
      Mix(BACK_CENTER, CENTER, kEqualPowerScale);
    }
  }

  // Mix LR of center into: front center || front LR.
  if (IsUnaccounted(LEFT_OF_CENTER)) {
    if (HasOutputChannel(LEFT)) {
      // Mix LR of center into front LR.
      Mix(LEFT_OF_CENTER, LEFT, kEqualPowerScale);
      Mix(RIGHT_OF_CENTER, RIGHT, kEqualPowerScale);
    } else {
      // Mix LR of center into front center.
      Mix(LEFT_OF_CENTER, CENTER, kEqualPowerScale);
      Mix(RIGHT_OF_CENTER, CENTER, kEqualPowerScale);
    }
  }

  // Mix LFE into: front LR || front center.
  if (IsUnaccounted(LFE)) {
    if (!HasOutputChannel(CENTER)) {
      // Mix LFE into front LR.
      MixWithoutAccounting(LFE, LEFT, kEqualPowerScale);
      Mix(LFE, RIGHT, kEqualPowerScale);
    } else {
      // Mix LFE into front center.
      Mix(LFE, CENTER, kEqualPowerScale);
    }
  }

  // All channels should now be accounted for.
  DCHECK(unaccounted_inputs_.empty());

  // See if the output |matrix_| is simply a remapping matrix.  If each input
  // channel maps to a single output channel we can simply remap.  Doing this
  // programmatically is less fragile than logic checks on channel mappings.
  for (int output_ch = 0; output_ch < output_channels_; ++output_ch) {
    int input_mappings = 0;
    for (int input_ch = 0; input_ch < input_channels_; ++input_ch) {
      // We can only remap if each row contains a single scale of 1.  I.e., each
      // output channel is mapped from a single unscaled input channel.
      if ((*matrix_)[output_ch][input_ch] != 1 || ++input_mappings > 1)
        return false;
    }
  }

  // If we've gotten here, |matrix_| is simply a remapping.
  return true;
}

ChannelMixer::~ChannelMixer() {}

void ChannelMixer::Transform(const AudioBus* input, AudioBus* output) {
  CHECK_EQ(matrix_.size(), static_cast<size_t>(output->channels()));
  CHECK_EQ(matrix_[0].size(), static_cast<size_t>(input->channels()));
  CHECK_EQ(input->frames(), output->frames());

  // Zero initialize |output| so we're accumulating from zero.
  output->Zero();

  // If we're just remapping we can simply copy the correct input to output.
  if (remapping_) {
    for (int output_ch = 0; output_ch < output->channels(); ++output_ch) {
      for (int input_ch = 0; input_ch < input->channels(); ++input_ch) {
        float scale = matrix_[output_ch][input_ch];
        if (scale > 0) {
          DCHECK_EQ(scale, 1.0f);
          memcpy(output->channel(output_ch), input->channel(input_ch),
                 sizeof(*output->channel(output_ch)) * output->frames());
          break;
        }
      }
    }
    return;
  }

  for (int output_ch = 0; output_ch < output->channels(); ++output_ch) {
    for (int input_ch = 0; input_ch < input->channels(); ++input_ch) {
      float scale = matrix_[output_ch][input_ch];
      // Scale should always be positive.  Don't bother scaling by zero.
      DCHECK_GE(scale, 0);
      if (scale > 0) {
        vector_math::FMAC(input->channel(input_ch), scale, output->frames(),
                          output->channel(output_ch));
      }
    }
  }
}

void MatrixBuilder::AccountFor(Channels ch) {
  unaccounted_inputs_.erase(std::find(
      unaccounted_inputs_.begin(), unaccounted_inputs_.end(), ch));
}

bool MatrixBuilder::IsUnaccounted(Channels ch) {
  return std::find(unaccounted_inputs_.begin(), unaccounted_inputs_.end(),
                   ch) != unaccounted_inputs_.end();
}

bool MatrixBuilder::HasInputChannel(Channels ch) {
  return ChannelOrder(input_layout_, ch) >= 0;
}

bool MatrixBuilder::HasOutputChannel(Channels ch) {
  return ChannelOrder(output_layout_, ch) >= 0;
}

void MatrixBuilder::Mix(Channels input_ch, Channels output_ch, float scale) {
  MixWithoutAccounting(input_ch, output_ch, scale);
  AccountFor(input_ch);
}

void MatrixBuilder::MixWithoutAccounting(Channels input_ch, Channels output_ch,
                                         float scale) {
  int input_ch_index = ChannelOrder(input_layout_, input_ch);
  int output_ch_index = ChannelOrder(output_layout_, output_ch);

  DCHECK(IsUnaccounted(input_ch));
  DCHECK_GE(input_ch_index, 0);
  DCHECK_GE(output_ch_index, 0);

  DCHECK_EQ((*matrix_)[output_ch_index][input_ch_index], 0);
  (*matrix_)[output_ch_index][input_ch_index] = scale;
}

}  // namespace media