media/base/channel_mixer.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // MSVC++ requires this to be set before any other includes to get M_SQRT1_2.
   6 #define _USE_MATH_DEFINES
   7
   8 #include "media/base/channel_mixer.h"
   9
  10 #include <algorithm>
  11 #include <cmath>
  12
  13 #include "base/logging.h"
  14 #include "media/audio/audio_parameters.h"
  15 #include "media/base/audio_bus.h"
  16 #include "media/base/vector_math.h"
  17
  18 namespace media {
  19
  20 // Default scale factor for mixing two channels together.  We use a different
  21 // value for stereo -> mono and mono -> stereo mixes.
  22 static const float kEqualPowerScale = static_cast<float>(M_SQRT1_2);
  23
  24 static void ValidateLayout(ChannelLayout layout) {
  25   CHECK_NE(layout, CHANNEL_LAYOUT_NONE);
  26   CHECK_NE(layout, CHANNEL_LAYOUT_MAX);
  27   CHECK_NE(layout, CHANNEL_LAYOUT_UNSUPPORTED);
  28   CHECK_NE(layout, CHANNEL_LAYOUT_DISCRETE);
  29
  30   // Verify there's at least one channel.  Should always be true here by virtue
  31   // of not being one of the invalid layouts, but lets double check to be sure.
  32   int channel_count = ChannelLayoutToChannelCount(layout);
  33   DCHECK_GT(channel_count, 0);
  34
  35   // If we have more than one channel, verify a symmetric layout for sanity.
  36   // The unit test will verify all possible layouts, so this can be a DCHECK.
  37   // Symmetry allows simplifying the matrix building code by allowing us to
  38   // assume that if one channel of a pair exists, the other will too.
  39   if (channel_count > 1) {
  40     DCHECK((ChannelOrder(layout, LEFT) >= 0 &&
  41             ChannelOrder(layout, RIGHT) >= 0) ||
  42            (ChannelOrder(layout, SIDE_LEFT) >= 0 &&
  43             ChannelOrder(layout, SIDE_RIGHT) >= 0) ||
  44            (ChannelOrder(layout, BACK_LEFT) >= 0 &&
  45             ChannelOrder(layout, BACK_RIGHT) >= 0) ||
  46            (ChannelOrder(layout, LEFT_OF_CENTER) >= 0 &&
  47             ChannelOrder(layout, RIGHT_OF_CENTER) >= 0))
  48         << "Non-symmetric channel layout encountered.";
  49   } else {
  50     DCHECK_EQ(layout, CHANNEL_LAYOUT_MONO);
  51   }
  52
  53   return;
  54 }
  55
  56 class MatrixBuilder {
  57  public:
  58   MatrixBuilder(ChannelLayout input_layout, int input_channels,
  59                 ChannelLayout output_layout, int output_channels)
  60       : input_layout_(input_layout),
  61         input_channels_(input_channels),
  62         output_layout_(output_layout),
  63         output_channels_(output_channels) {
  64     // Special case for 5.0, 5.1 with back channels when upmixed to 7.0, 7.1,
  65     // which should map the back LR to side LR.
  66     if (input_layout_ == CHANNEL_LAYOUT_5_0_BACK &&
  67         output_layout_ == CHANNEL_LAYOUT_7_0) {
  68       input_layout_ = CHANNEL_LAYOUT_5_0;
  69     } else if (input_layout_ == CHANNEL_LAYOUT_5_1_BACK &&
  70                output_layout_ == CHANNEL_LAYOUT_7_1) {
  71       input_layout_ = CHANNEL_LAYOUT_5_1;
  72     }
  73   }
  74
  75   ~MatrixBuilder() { }
  76
  77   // Create the transformation matrix of input channels to output channels.
  78   // Updates the empty matrix with the transformation, and returns true
  79   // if the transformation is just a remapping of channels (no mixing).
  80   bool CreateTransformationMatrix(std::vector< std::vector<float> >* matrix);
  81
  82  private:
  83   // Result transformation of input channels to output channels
  84   std::vector< std::vector<float> >* matrix_;
  85
  86   // Input and output channel layout provided during construction.
  87   ChannelLayout input_layout_;
  88   int input_channels_;
  89   ChannelLayout output_layout_;
  90   int output_channels_;
  91
  92   // Helper variable for tracking which inputs are currently unaccounted,
  93   // should be empty after construction completes.
  94   std::vector<Channels> unaccounted_inputs_;
  95
  96   // Helper methods for managing unaccounted input channels.
  97   void AccountFor(Channels ch);
  98   bool IsUnaccounted(Channels ch);
  99
 100   // Helper methods for checking if |ch| exists in either |input_layout_| or
 101   // |output_layout_| respectively.
 102   bool HasInputChannel(Channels ch);
 103   bool HasOutputChannel(Channels ch);
 104
 105   // Helper methods for updating |matrix_| with the proper value for
 106   // mixing |input_ch| into |output_ch|.  MixWithoutAccounting() does not
 107   // remove the channel from |unaccounted_inputs_|.
 108   void Mix(Channels input_ch, Channels output_ch, float scale);
 109   void MixWithoutAccounting(Channels input_ch, Channels output_ch,
 110                                           float scale);
 111
 112   DISALLOW_COPY_AND_ASSIGN(MatrixBuilder);
 113 };
 114
 115 ChannelMixer::ChannelMixer(ChannelLayout input_layout,
 116                            ChannelLayout output_layout) {
 117   Initialize(input_layout,
 118              ChannelLayoutToChannelCount(input_layout),
 119              output_layout,
 120              ChannelLayoutToChannelCount(output_layout));
 121 }
 122
 123 ChannelMixer::ChannelMixer(
 124     const AudioParameters& input, const AudioParameters& output) {
 125   Initialize(input.channel_layout(),
 126              input.channels(),
 127              output.channel_layout(),
 128              output.channels());
 129 }
 130
 131 void ChannelMixer::Initialize(
 132     ChannelLayout input_layout, int input_channels,
 133     ChannelLayout output_layout, int output_channels) {
 134   // Stereo down mix should never be the output layout.
 135   CHECK_NE(output_layout, CHANNEL_LAYOUT_STEREO_DOWNMIX);
 136
 137   // Verify that the layouts are supported
 138   if (input_layout != CHANNEL_LAYOUT_DISCRETE)
 139     ValidateLayout(input_layout);
 140   if (output_layout != CHANNEL_LAYOUT_DISCRETE)
 141     ValidateLayout(output_layout);
 142
 143   // Create the transformation matrix
 144   MatrixBuilder matrix_builder(input_layout, input_channels,
 145                                output_layout, output_channels);
 146   remapping_ = matrix_builder.CreateTransformationMatrix(&matrix_);
 147 }
 148
 149 bool MatrixBuilder::CreateTransformationMatrix(
 150     std::vector< std::vector<float> >* matrix) {
 151   matrix_ = matrix;
 152
 153   // Size out the initial matrix.
 154   matrix_->reserve(output_channels_);
 155   for (int output_ch = 0; output_ch < output_channels_; ++output_ch)
 156     matrix_->push_back(std::vector<float>(input_channels_, 0));
 157
 158   // First check for discrete case.
 159   if (input_layout_ == CHANNEL_LAYOUT_DISCRETE ||
 160       output_layout_ == CHANNEL_LAYOUT_DISCRETE) {
 161     // If the number of input channels is more than output channels, then
 162     // copy as many as we can then drop the remaining input channels.
 163     // If the number of input channels is less than output channels, then
 164     // copy them all, then zero out the remaining output channels.
 165     int passthrough_channels = std::min(input_channels_, output_channels_);
 166     for (int i = 0; i < passthrough_channels; ++i)
 167       (*matrix_)[i][i] = 1;
 168
 169     return true;
 170   }
 171
 172   // Route matching channels and figure out which ones aren't accounted for.
 173   for (Channels ch = LEFT; ch < CHANNELS_MAX;
 174        ch = static_cast<Channels>(ch + 1)) {
 175     int input_ch_index = ChannelOrder(input_layout_, ch);
 176     if (input_ch_index < 0)
 177       continue;
 178
 179     int output_ch_index = ChannelOrder(output_layout_, ch);
 180     if (output_ch_index < 0) {
 181       unaccounted_inputs_.push_back(ch);
 182       continue;
 183     }
 184
 185     DCHECK_LT(static_cast<size_t>(output_ch_index), matrix_->size());
 186     DCHECK_LT(static_cast<size_t>(input_ch_index),
 187               (*matrix_)[output_ch_index].size());
 188     (*matrix_)[output_ch_index][input_ch_index] = 1;
 189   }
 190
 191   // If all input channels are accounted for, there's nothing left to do.
 192   if (unaccounted_inputs_.empty()) {
 193     // Since all output channels map directly to inputs we can optimize.
 194     return true;
 195   }
 196
 197   // Mix front LR into center.
 198   if (IsUnaccounted(LEFT)) {
 199     // When down mixing to mono from stereo, we need to be careful of full scale
 200     // stereo mixes.  Scaling by 1 / sqrt(2) here will likely lead to clipping
 201     // so we use 1 / 2 instead.
 202     float scale =
 203         (output_layout_ == CHANNEL_LAYOUT_MONO && input_channels_ == 2) ?
 204         0.5 : kEqualPowerScale;
 205     Mix(LEFT, CENTER, scale);
 206     Mix(RIGHT, CENTER, scale);
 207   }
 208
 209   // Mix center into front LR.
 210   if (IsUnaccounted(CENTER)) {
 211     // When up mixing from mono, just do a copy to front LR.
 212     float scale =
 213         (input_layout_ == CHANNEL_LAYOUT_MONO) ? 1 : kEqualPowerScale;
 214     MixWithoutAccounting(CENTER, LEFT, scale);
 215     Mix(CENTER, RIGHT, scale);
 216   }
 217
 218   // Mix back LR into: side LR || back center || front LR || front center.
 219   if (IsUnaccounted(BACK_LEFT)) {
 220     if (HasOutputChannel(SIDE_LEFT)) {
 221       // If we have side LR, mix back LR into side LR, but instead if the input
 222       // doesn't have side LR (but output does) copy back LR to side LR.
 223       float scale = HasInputChannel(SIDE_LEFT) ? kEqualPowerScale : 1;
 224       Mix(BACK_LEFT, SIDE_LEFT, scale);
 225       Mix(BACK_RIGHT, SIDE_RIGHT, scale);
 226     } else if (HasOutputChannel(BACK_CENTER)) {
 227       // Mix back LR into back center.
 228       Mix(BACK_LEFT, BACK_CENTER, kEqualPowerScale);
 229       Mix(BACK_RIGHT, BACK_CENTER, kEqualPowerScale);
 230     } else if (output_layout_ > CHANNEL_LAYOUT_MONO) {
 231       // Mix back LR into front LR.
 232       Mix(BACK_LEFT, LEFT, kEqualPowerScale);
 233       Mix(BACK_RIGHT, RIGHT, kEqualPowerScale);
 234     } else {
 235       // Mix back LR into front center.
 236       Mix(BACK_LEFT, CENTER, kEqualPowerScale);
 237       Mix(BACK_RIGHT, CENTER, kEqualPowerScale);
 238     }
 239   }
 240
 241   // Mix side LR into: back LR || back center || front LR || front center.
 242   if (IsUnaccounted(SIDE_LEFT)) {
 243     if (HasOutputChannel(BACK_LEFT)) {
 244       // If we have back LR, mix side LR into back LR, but instead if the input
 245       // doesn't have back LR (but output does) copy side LR to back LR.
 246       float scale = HasInputChannel(BACK_LEFT) ? kEqualPowerScale : 1;
 247       Mix(SIDE_LEFT, BACK_LEFT, scale);
 248       Mix(SIDE_RIGHT, BACK_RIGHT, scale);
 249     } else if (HasOutputChannel(BACK_CENTER)) {
 250       // Mix side LR into back center.
 251       Mix(SIDE_LEFT, BACK_CENTER, kEqualPowerScale);
 252       Mix(SIDE_RIGHT, BACK_CENTER, kEqualPowerScale);
 253     } else if (output_layout_ > CHANNEL_LAYOUT_MONO) {
 254       // Mix side LR into front LR.
 255       Mix(SIDE_LEFT, LEFT, kEqualPowerScale);
 256       Mix(SIDE_RIGHT, RIGHT, kEqualPowerScale);
 257     } else {
 258       // Mix side LR into front center.
 259       Mix(SIDE_LEFT, CENTER, kEqualPowerScale);
 260       Mix(SIDE_RIGHT, CENTER, kEqualPowerScale);
 261     }
 262   }
 263
 264   // Mix back center into: back LR || side LR || front LR || front center.
 265   if (IsUnaccounted(BACK_CENTER)) {
 266     if (HasOutputChannel(BACK_LEFT)) {
 267       // Mix back center into back LR.
 268       MixWithoutAccounting(BACK_CENTER, BACK_LEFT, kEqualPowerScale);
 269       Mix(BACK_CENTER, BACK_RIGHT, kEqualPowerScale);
 270     } else if (HasOutputChannel(SIDE_LEFT)) {
 271       // Mix back center into side LR.
 272       MixWithoutAccounting(BACK_CENTER, SIDE_LEFT, kEqualPowerScale);
 273       Mix(BACK_CENTER, SIDE_RIGHT, kEqualPowerScale);
 274     } else if (output_layout_ > CHANNEL_LAYOUT_MONO) {
 275       // Mix back center into front LR.
 276       // TODO(dalecurtis): Not sure about these values?
 277       MixWithoutAccounting(BACK_CENTER, LEFT, kEqualPowerScale);
 278       Mix(BACK_CENTER, RIGHT, kEqualPowerScale);
 279     } else {
 280       // Mix back center into front center.
 281       // TODO(dalecurtis): Not sure about these values?
 282       Mix(BACK_CENTER, CENTER, kEqualPowerScale);
 283     }
 284   }
 285
 286   // Mix LR of center into: front center || front LR.
 287   if (IsUnaccounted(LEFT_OF_CENTER)) {
 288     if (HasOutputChannel(LEFT)) {
 289       // Mix LR of center into front LR.
 290       Mix(LEFT_OF_CENTER, LEFT, kEqualPowerScale);
 291       Mix(RIGHT_OF_CENTER, RIGHT, kEqualPowerScale);
 292     } else {
 293       // Mix LR of center into front center.
 294       Mix(LEFT_OF_CENTER, CENTER, kEqualPowerScale);
 295       Mix(RIGHT_OF_CENTER, CENTER, kEqualPowerScale);
 296     }
 297   }
 298
 299   // Mix LFE into: front LR || front center.
 300   if (IsUnaccounted(LFE)) {
 301     if (!HasOutputChannel(CENTER)) {
 302       // Mix LFE into front LR.
 303       MixWithoutAccounting(LFE, LEFT, kEqualPowerScale);
 304       Mix(LFE, RIGHT, kEqualPowerScale);
 305     } else {
 306       // Mix LFE into front center.
 307       Mix(LFE, CENTER, kEqualPowerScale);
 308     }
 309   }
 310
 311   // All channels should now be accounted for.
 312   DCHECK(unaccounted_inputs_.empty());
 313
 314   // See if the output |matrix_| is simply a remapping matrix.  If each input
 315   // channel maps to a single output channel we can simply remap.  Doing this
 316   // programmatically is less fragile than logic checks on channel mappings.
 317   for (int output_ch = 0; output_ch < output_channels_; ++output_ch) {
 318     int input_mappings = 0;
 319     for (int input_ch = 0; input_ch < input_channels_; ++input_ch) {
 320       // We can only remap if each row contains a single scale of 1.  I.e., each
 321       // output channel is mapped from a single unscaled input channel.
 322       if ((*matrix_)[output_ch][input_ch] != 1 || ++input_mappings > 1)
 323         return false;
 324     }
 325   }
 326
 327   // If we've gotten here, |matrix_| is simply a remapping.
 328   return true;
 329 }
 330
 331 ChannelMixer::~ChannelMixer() {}
 332
 333 void ChannelMixer::Transform(const AudioBus* input, AudioBus* output) {
 334   CHECK_EQ(matrix_.size(), static_cast<size_t>(output->channels()));
 335   CHECK_EQ(matrix_[0].size(), static_cast<size_t>(input->channels()));
 336   CHECK_EQ(input->frames(), output->frames());
 337
 338   // Zero initialize |output| so we're accumulating from zero.
 339   output->Zero();
 340
 341   // If we're just remapping we can simply copy the correct input to output.
 342   if (remapping_) {
 343     for (int output_ch = 0; output_ch < output->channels(); ++output_ch) {
 344       for (int input_ch = 0; input_ch < input->channels(); ++input_ch) {
 345         float scale = matrix_[output_ch][input_ch];
 346         if (scale > 0) {
 347           DCHECK_EQ(scale, 1.0f);
 348           memcpy(output->channel(output_ch), input->channel(input_ch),
 349                  sizeof(*output->channel(output_ch)) * output->frames());
 350           break;
 351         }
 352       }
 353     }
 354     return;
 355   }
 356
 357   for (int output_ch = 0; output_ch < output->channels(); ++output_ch) {
 358     for (int input_ch = 0; input_ch < input->channels(); ++input_ch) {
 359       float scale = matrix_[output_ch][input_ch];
 360       // Scale should always be positive.  Don't bother scaling by zero.
 361       DCHECK_GE(scale, 0);
 362       if (scale > 0) {
 363         vector_math::FMAC(input->channel(input_ch), scale, output->frames(),
 364                           output->channel(output_ch));
 365       }
 366     }
 367   }
 368 }
 369
 370 void MatrixBuilder::AccountFor(Channels ch) {
 371   unaccounted_inputs_.erase(std::find(
 372       unaccounted_inputs_.begin(), unaccounted_inputs_.end(), ch));
 373 }
 374
 375 bool MatrixBuilder::IsUnaccounted(Channels ch) {
 376   return std::find(unaccounted_inputs_.begin(), unaccounted_inputs_.end(),
 377                    ch) != unaccounted_inputs_.end();
 378 }
 379
 380 bool MatrixBuilder::HasInputChannel(Channels ch) {
 381   return ChannelOrder(input_layout_, ch) >= 0;
 382 }
 383
 384 bool MatrixBuilder::HasOutputChannel(Channels ch) {
 385   return ChannelOrder(output_layout_, ch) >= 0;
 386 }
 387
 388 void MatrixBuilder::Mix(Channels input_ch, Channels output_ch, float scale) {
 389   MixWithoutAccounting(input_ch, output_ch, scale);
 390   AccountFor(input_ch);
 391 }
 392
 393 void MatrixBuilder::MixWithoutAccounting(Channels input_ch, Channels output_ch,
 394                                          float scale) {
 395   int input_ch_index = ChannelOrder(input_layout_, input_ch);
 396   int output_ch_index = ChannelOrder(output_layout_, output_ch);
 397
 398   DCHECK(IsUnaccounted(input_ch));
 399   DCHECK_GE(input_ch_index, 0);
 400   DCHECK_GE(output_ch_index, 0);
 401
 402   DCHECK_EQ((*matrix_)[output_ch_index][input_ch_index], 0);
 403   (*matrix_)[output_ch_index][input_ch_index] = scale;
 404 }
 405
 406 }  // namespace media