Switch to pcm_low_latency and enable resampling.

media/base/audio_renderer_mixer_unittest.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_PI.
+#define _USE_MATH_DEFINES
 #include <cmath>
 
 #include "base/memory/scoped_ptr.h"
-#include "media/audio/audio_util.h"
+#include "base/memory/scoped_vector.h"
 #include "media/base/audio_renderer_mixer.h"
 #include "media/base/audio_renderer_mixer_input.h"
 #include "media/base/fake_audio_render_callback.h"
+#include "media/base/mock_audio_renderer_sink.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace media {
 
 // Parameters which control the many input case tests.
-static const int kMixerInputs = 64;
-static const int kMixerCycles = 32;
+static const int kMixerInputs = 8;
+static const int kMixerCycles = 3;
 
+// Parameters used for testing.
 static const int kBitsPerChannel = 16;
-static const int kSampleRate = 48000;
 static const ChannelLayout kChannelLayout = CHANNEL_LAYOUT_STEREO;
+static const int kHighLatencyBufferSize = 8192;
+static const int kLowLatencyBufferSize = 256;
 
-// Multiple rounds of addition result in precision loss with float values, so we
-// need an epsilon such that if for all x f(x) = sum(x, m) and g(x) = m * x then
-// fabs(f - g) < kEpsilon.  The kEpsilon below has been tested with m < 128.
-static const float kEpsilon = 0.00015f;
+// Number of full sine wave cycles for each Render() call.
+static const int kSineCycles = 4;
 
-class MockAudioRendererSink : public AudioRendererSink {
+typedef std::tr1::tuple<int, int, double> AudioRendererMixerTestData;

[scherkus (not reviewing), 2012/07/12 23:02:52]

AFAIK a struct *should* work here instead, which makes for easier-to-read code
(std::tr1::get<1> vs output_sample_rate)

struct ARMTD {
  int input_sample_rate;
  int output_sample_rate;
  double epsilon;
};

[DaleCurtis, 2012/07/12 23:16:29]

I don't think we'd get nice error messages then. It'd be "where GetParam() = 12
byte<00-00-00-00 ..." etc.

[DaleCurtis, 2012/07/13 00:01:25]

Confirmed. I'll need to add an ostream() operator override for the struct to go
this route.

[scherkus (not reviewing), 2012/07/14 01:45:02]

yeah that's what I figured -- your call

I wonder if tr1 usage will compile everywhere but I guess we'll find out! I only
see 2 instances in all of chrome (!), which suggests to me it isn't too common
(both seem to be for parameterized tests, so I guess it's not too foreign of a
concept):
http://code.google.com/p/chromium/source/search?q=tr1%3A%3Atuple+-file%3Athir...

+class AudioRendererMixerTestCase
+    : public testing::TestWithParam<AudioRendererMixerTestData> {
  public:
-  MOCK_METHOD0(Start, void());
-  MOCK_METHOD0(Stop, void());
-  MOCK_METHOD1(Pause, void(bool flush));
-  MOCK_METHOD0(Play, void());
-  MOCK_METHOD1(SetPlaybackRate, void(float rate));
-  MOCK_METHOD1(SetVolume, bool(double volume));
-  MOCK_METHOD1(GetVolume, void(double* volume));
+  AudioRendererMixerTestCase()
+      : epsilon_(std::tr1::get<2>(GetParam())),
+        half_fill_(false) {
+    // Create input and output parameters based on test parameters.
+    input_parameters_ = AudioParameters(
+        AudioParameters::AUDIO_PCM_LINEAR, kChannelLayout,
+        std::tr1::get<0>(GetParam()), kBitsPerChannel, kHighLatencyBufferSize);
+    output_parameters_ = AudioParameters(
+        AudioParameters::AUDIO_PCM_LOW_LATENCY, kChannelLayout,
+        std::tr1::get<1>(GetParam()), 16, kLowLatencyBufferSize);
 
-  void Initialize(const media::AudioParameters& params,
-                  AudioRendererSink::RenderCallback* renderer) OVERRIDE {
-    // TODO(dalecurtis): Once we have resampling we need to ensure we are given
-    // an AudioParameters which reflects the hardware settings.
-    callback_ = renderer;
-  };
-
-  AudioRendererSink::RenderCallback* callback() {
-    return callback_;
-  }
-
-  void SimulateRenderError() {
-    callback_->OnRenderError();
-  }
-
- protected:
-  virtual ~MockAudioRendererSink() {}
-
-  AudioRendererSink::RenderCallback* callback_;
-};
-
-class AudioRendererMixerTest : public ::testing::Test {
- public:
-  AudioRendererMixerTest() {
-    audio_parameters_ = AudioParameters(
-        AudioParameters::AUDIO_PCM_LINEAR, kChannelLayout, kSampleRate,
-        kBitsPerChannel, GetHighLatencyOutputBufferSize(kSampleRate));
     sink_ = new MockAudioRendererSink();
     EXPECT_CALL(*sink_, Start());
     EXPECT_CALL(*sink_, Stop());
 
-    mixer_ = new AudioRendererMixer(audio_parameters_, sink_);
+    mixer_ = new AudioRendererMixer(
+        input_parameters_, output_parameters_, sink_);
     mixer_callback_ = sink_->callback();
 
     // TODO(dalecurtis): If we switch to AVX/SSE optimization, we'll need to
     // allocate these on 32-byte boundaries and ensure they're sized % 32 bytes.
-    audio_data_.reserve(audio_parameters_.channels());
-    for (int i = 0; i < audio_parameters_.channels(); ++i)
-      audio_data_.push_back(new float[audio_parameters_.frames_per_buffer()]);
+    audio_data_.reserve(output_parameters_.channels());
+    for (int i = 0; i < output_parameters_.channels(); ++i)
+      audio_data_.push_back(new float[output_parameters_.frames_per_buffer()]);
 
-    fake_callback_.reset(new FakeAudioRenderCallback(audio_parameters_));
+    // TODO(dalecurtis): If we switch to AVX/SSE optimization, we'll need to
+    // allocate these on 32-byte boundaries and ensure they're sized % 32 bytes.
+    expected_audio_data_.reserve(output_parameters_.channels());
+    for (int i = 0; i < output_parameters_.channels(); ++i) {
+      expected_audio_data_.push_back(
+          new float[output_parameters_.frames_per_buffer()]);
+    }
+
+    // Allocate one callback for generating expected results.
+    double step = kSineCycles / static_cast<double>(
+        output_parameters_.frames_per_buffer());
+    expected_callback_.reset(new FakeAudioRenderCallback(step));
   }
 
   void InitializeInputs(int count) {
+    mixer_inputs_.reserve(count);
+    fake_callbacks_.reserve(count);
+
+    // Setup FakeAudioRenderCallback step to compensate for resampling.
+    double scale_factor = input_parameters_.sample_rate()
+        / static_cast<double>(output_parameters_.sample_rate());
+    double step = kSineCycles / (scale_factor *
+        static_cast<double>(output_parameters_.frames_per_buffer()));
+
     for (int i = 0; i < count; ++i) {
-      scoped_refptr<AudioRendererMixerInput> mixer_input(
-          new AudioRendererMixerInput(mixer_));
-      mixer_input->Initialize(audio_parameters_, fake_callback_.get());
-      mixer_input->SetVolume(1.0f);
-      mixer_inputs_.push_back(mixer_input);
+      fake_callbacks_.push_back(new FakeAudioRenderCallback(step));
+      mixer_inputs_.push_back(new AudioRendererMixerInput(mixer_));
+      mixer_inputs_[i]->Initialize(input_parameters_, fake_callbacks_[i]);
+      mixer_inputs_[i]->SetVolume(1.0f);
     }
   }
 
-  bool ValidateAudioData(int start_index, int frames, float check_value) {
+  bool ValidateAudioData(int index, int frames, float scale) {
     for (size_t i = 0; i < audio_data_.size(); ++i) {
-      for (int j = start_index; j < frames; j++) {
-        if (fabs(audio_data_[i][j] - check_value) > kEpsilon) {
-          EXPECT_NEAR(check_value, audio_data_[i][j], kEpsilon)
+      for (int j = index; j < frames; j++) {
+        double error = fabs(
+            audio_data_[i][j] - expected_audio_data_[i][j] * scale);
+        if (error > epsilon_) {
+          EXPECT_NEAR(
+              expected_audio_data_[i][j] * scale, audio_data_[i][j], epsilon_)
               << " i=" << i << ", j=" << j;
           return false;
         }
       }
     }
     return true;
   }
 
-  // Render audio_parameters_.frames_per_buffer() frames into |audio_data_| and
-  // verify the result against |check_value|.
-  bool RenderAndValidateAudioData(float check_value) {
-    int frames = mixer_callback_->Render(
-        audio_data_, audio_parameters_.frames_per_buffer(), 0);
-    return frames == audio_parameters_.frames_per_buffer() && ValidateAudioData(
-        0, audio_parameters_.frames_per_buffer(), check_value);
+  bool RenderAndValidateAudioData(float scale) {
+    int request_frames = output_parameters_.frames_per_buffer();
+
+    // Half fill won't be exactly half when resampling since the resampler
+    // will have enough data to fill out more of the buffer based on its
+    // internal buffer and kernel size.  So special case some of the checks.
+    bool resampling = input_parameters_.sample_rate()
+        != output_parameters_.sample_rate();
+
+    if (half_fill_) {
+      for (size_t i = 0; i < fake_callbacks_.size(); ++i)
+        fake_callbacks_[i]->set_half_fill(true);
+      expected_callback_->set_half_fill(true);
+    }
+
+    // Render actual audio data.
+    int frames = mixer_callback_->Render(audio_data_, request_frames, 0);
+    if (frames != request_frames)
+      return false;
+
+    // Render expected audio data (without scaling).
+    expected_callback_->Render(expected_audio_data_, request_frames, 0);
+
+    if (half_fill_) {
+      // Verify first half of audio data for both resampling and non-resampling.
+      if (!ValidateAudioData(0, frames / 2, scale))
+        return false;
+      // Verify silence in the second half if we're not resampling.
+      if (!resampling)
+        return ValidateAudioData(frames / 2, frames, 0);
+      return true;
+    } else {
+      return ValidateAudioData(0, frames, scale);
+    }
   }
 
   // Fill |audio_data_| fully with |value|.
   void FillAudioData(float value) {
     for (size_t i = 0; i < audio_data_.size(); ++i)
       std::fill(audio_data_[i],
-                audio_data_[i] + audio_parameters_.frames_per_buffer(), value);
+                audio_data_[i] + output_parameters_.frames_per_buffer(), value);
   }
 
   // Verify silence when mixer inputs are in pre-Start() and post-Start().
   void StartTest(int inputs) {
     InitializeInputs(inputs);
 
     // Verify silence before any inputs have been started.  Fill the buffer
     // before hand with non-zero data to ensure we get zeros back.
     FillAudioData(1.0f);
     EXPECT_TRUE(RenderAndValidateAudioData(0.0f));
@@ skipping 11 matching lines @@
     EXPECT_TRUE(RenderAndValidateAudioData(0.0f));
 
     for (size_t i = 0; i < mixer_inputs_.size(); ++i)
       mixer_inputs_[i]->Stop();
   }
 
   // Verify output when mixer inputs are in post-Play() state.
   void PlayTest(int inputs) {
     InitializeInputs(inputs);
 
-    for (size_t i = 0; i < mixer_inputs_.size(); ++i)
+    // Play() all mixer inputs and ensure we get the right values.
+    for (size_t i = 0; i < mixer_inputs_.size(); ++i) {
       mixer_inputs_[i]->Start();
-
-    // Play() all even numbered mixer inputs and ensure we get the right value.
-    for (size_t i = 0; i < mixer_inputs_.size(); i += 2)
       mixer_inputs_[i]->Play();
-    for (int i = 0; i < kMixerCycles; ++i) {
-      fake_callback_->NextFillValue();
-      ASSERT_TRUE(RenderAndValidateAudioData(
-          fake_callback_->fill_value() * std::max(
-              mixer_inputs_.size() / 2, static_cast<size_t>(1))));
     }
 
-    // Play() all mixer inputs and ensure we still get the right values.
-    for (size_t i = 1; i < mixer_inputs_.size(); i += 2)
-      mixer_inputs_[i]->Play();
-    for (int i = 0; i < kMixerCycles; ++i) {
-      fake_callback_->NextFillValue();
-      ASSERT_TRUE(RenderAndValidateAudioData(
-          fake_callback_->fill_value() * mixer_inputs_.size()));
-    }
+    for (int i = 0; i < kMixerCycles; ++i)
+      ASSERT_TRUE(RenderAndValidateAudioData(mixer_inputs_.size()));
 
     for (size_t i = 0; i < mixer_inputs_.size(); ++i)
       mixer_inputs_[i]->Stop();
   }
 
   // Verify volume adjusted output when mixer inputs are in post-Play() state.
   void PlayVolumeAdjustedTest(int inputs) {
     InitializeInputs(inputs);
 
     for (size_t i = 0; i < mixer_inputs_.size(); ++i) {
       mixer_inputs_[i]->Start();
       mixer_inputs_[i]->Play();
     }
 
     // Set a different volume for each mixer input and verify the results.
     float total_scale = 0;
     for (size_t i = 0; i < mixer_inputs_.size(); ++i) {
       float volume = static_cast<float>(i) / mixer_inputs_.size();
       total_scale += volume;
       EXPECT_TRUE(mixer_inputs_[i]->SetVolume(volume));
     }
-    for (int i = 0; i < kMixerCycles; ++i) {
-      fake_callback_->NextFillValue();
-      ASSERT_TRUE(RenderAndValidateAudioData(
-          fake_callback_->fill_value() * total_scale));
-    }
+    for (int i = 0; i < kMixerCycles; ++i)
+      ASSERT_TRUE(RenderAndValidateAudioData(total_scale));
 
     for (size_t i = 0; i < mixer_inputs_.size(); ++i)
       mixer_inputs_[i]->Stop();
   }
 
   // Verify output when mixer inputs can only partially fulfill a Render().
   void PlayPartialRenderTest(int inputs) {
     InitializeInputs(inputs);
-    int frames = audio_parameters_.frames_per_buffer();
 
     for (size_t i = 0; i < mixer_inputs_.size(); ++i) {
       mixer_inputs_[i]->Start();
       mixer_inputs_[i]->Play();
     }
 
     // Verify a properly filled buffer when half filled (remainder zeroed).
-    fake_callback_->set_half_fill(true);
-    for (int i = 0; i < kMixerCycles; ++i) {
-      fake_callback_->NextFillValue();
-      ASSERT_EQ(mixer_callback_->Render(audio_data_, frames, 0), frames);
-      ASSERT_TRUE(ValidateAudioData(
-          0, frames / 2, fake_callback_->fill_value() * mixer_inputs_.size()));
-      ASSERT_TRUE(ValidateAudioData(
-          frames / 2, frames, 0.0f));
-    }
-    fake_callback_->set_half_fill(false);
+    half_fill_ = true;
+    ASSERT_TRUE(RenderAndValidateAudioData(mixer_inputs_.size()));
 
     for (size_t i = 0; i < mixer_inputs_.size(); ++i)
       mixer_inputs_[i]->Stop();
   }
 
   // Verify output when mixer inputs are in Pause() state.
   void PauseTest(int inputs) {
     InitializeInputs(inputs);
 
     for (size_t i = 0; i < mixer_inputs_.size(); ++i) {
       mixer_inputs_[i]->Start();
       mixer_inputs_[i]->Play();
     }
 
     // Pause() all even numbered mixer inputs and ensure we get the right value.
     for (size_t i = 0; i < mixer_inputs_.size(); i += 2)
       mixer_inputs_[i]->Pause(false);
-    for (int i = 0; i < kMixerCycles; ++i) {
-      fake_callback_->NextFillValue();
-      ASSERT_TRUE(RenderAndValidateAudioData(
-          fake_callback_->fill_value() * (mixer_inputs_.size() / 2)));
-    }
-
-    // Pause() all the inputs and verify we get silence back.
-    for (size_t i = 1; i < mixer_inputs_.size(); i += 2)
-      mixer_inputs_[i]->Pause(false);
-    FillAudioData(1.0f);
-    EXPECT_TRUE(RenderAndValidateAudioData(0.0f));
+    for (int i = 0; i < kMixerCycles; ++i)
+      ASSERT_TRUE(RenderAndValidateAudioData(mixer_inputs_.size() / 2));
 
     for (size_t i = 0; i < mixer_inputs_.size(); ++i)
       mixer_inputs_[i]->Stop();
   }
 
   // Verify output when mixer inputs are in post-Stop() state.
   void StopTest(int inputs) {
     InitializeInputs(inputs);
 
     // Start() and Stop() all inputs.
     for (size_t i = 0; i < mixer_inputs_.size(); ++i) {
       mixer_inputs_[i]->Start();
       mixer_inputs_[i]->Stop();
     }
 
     // Verify we get silence back; fill |audio_data_| before hand to be sure.
     FillAudioData(1.0f);
     EXPECT_TRUE(RenderAndValidateAudioData(0.0f));
   }
 
  protected:
-  virtual ~AudioRendererMixerTest() {
+  virtual ~AudioRendererMixerTestCase() {
     for (size_t i = 0; i < audio_data_.size(); ++i)
       delete [] audio_data_[i];
   }
 
   scoped_refptr<MockAudioRendererSink> sink_;
   scoped_refptr<AudioRendererMixer> mixer_;
   AudioRendererSink::RenderCallback* mixer_callback_;
-  scoped_ptr<FakeAudioRenderCallback> fake_callback_;
-  AudioParameters audio_parameters_;
+  AudioParameters input_parameters_;
+  AudioParameters output_parameters_;
   std::vector<float*> audio_data_;
+  std::vector<float*> expected_audio_data_;
   std::vector< scoped_refptr<AudioRendererMixerInput> > mixer_inputs_;
+  ScopedVector<FakeAudioRenderCallback> fake_callbacks_;
+  scoped_ptr<FakeAudioRenderCallback> expected_callback_;
+  double epsilon_;
+  bool half_fill_;
 
-  DISALLOW_COPY_AND_ASSIGN(AudioRendererMixerTest);
+  DISALLOW_COPY_AND_ASSIGN(AudioRendererMixerTestCase);
 };
 
 // Verify a mixer with no inputs returns silence for all requested frames.
-TEST_F(AudioRendererMixerTest, NoInputs) {
+TEST_P(AudioRendererMixerTestCase, NoInputs) {
   FillAudioData(1.0f);
   EXPECT_TRUE(RenderAndValidateAudioData(0.0f));
 }
 
 // Test mixer output with one input in the pre-Start() and post-Start() state.
-TEST_F(AudioRendererMixerTest, OneInputStart) {
+TEST_P(AudioRendererMixerTestCase, OneInputStart) {
   StartTest(1);
 }
 
 // Test mixer output with many inputs in the pre-Start() and post-Start() state.
-TEST_F(AudioRendererMixerTest, ManyInputStart) {
+TEST_P(AudioRendererMixerTestCase, ManyInputStart) {
   StartTest(kMixerInputs);
 }
 
 // Test mixer output with one input in the post-Play() state.
-TEST_F(AudioRendererMixerTest, OneInputPlay) {
+TEST_P(AudioRendererMixerTestCase, OneInputPlay) {
   PlayTest(1);
 }
 
 // Test mixer output with many inputs in the post-Play() state.
-TEST_F(AudioRendererMixerTest, ManyInputPlay) {
+TEST_P(AudioRendererMixerTestCase, ManyInputPlay) {
   PlayTest(kMixerInputs);
 }
 
 // Test volume adjusted mixer output with one input in the post-Play() state.
-TEST_F(AudioRendererMixerTest, OneInputPlayVolumeAdjusted) {
+TEST_P(AudioRendererMixerTestCase, OneInputPlayVolumeAdjusted) {
   PlayVolumeAdjustedTest(1);
 }
 
 // Test volume adjusted mixer output with many inputs in the post-Play() state.
-TEST_F(AudioRendererMixerTest, ManyInputPlayVolumeAdjusted) {
+TEST_P(AudioRendererMixerTestCase, ManyInputPlayVolumeAdjusted) {
   PlayVolumeAdjustedTest(kMixerInputs);
 }
 
 // Test mixer output with one input and partial Render() in post-Play() state.
-TEST_F(AudioRendererMixerTest, OneInputPlayPartialRender) {
+TEST_P(AudioRendererMixerTestCase, OneInputPlayPartialRender) {
   PlayPartialRenderTest(1);
 }
 
 // Test mixer output with many inputs and partial Render() in post-Play() state.
-TEST_F(AudioRendererMixerTest, ManyInputPlayPartialRender) {
+TEST_P(AudioRendererMixerTestCase, ManyInputPlayPartialRender) {
   PlayPartialRenderTest(kMixerInputs);
 }
 
 // Test mixer output with one input in the post-Pause() state.
-TEST_F(AudioRendererMixerTest, OneInputPause) {
+TEST_P(AudioRendererMixerTestCase, OneInputPause) {
   PauseTest(1);
 }
 
 // Test mixer output with many inputs in the post-Pause() state.
-TEST_F(AudioRendererMixerTest, ManyInputPause) {
+TEST_P(AudioRendererMixerTestCase, ManyInputPause) {
   PauseTest(kMixerInputs);
 }
 
 // Test mixer output with one input in the post-Stop() state.
-TEST_F(AudioRendererMixerTest, OneInputStop) {
+TEST_P(AudioRendererMixerTestCase, OneInputStop) {
   StopTest(1);
 }
 
 // Test mixer output with many inputs in the post-Stop() state.
-TEST_F(AudioRendererMixerTest, ManyInputStop) {
+TEST_P(AudioRendererMixerTestCase, ManyInputStop) {
   StopTest(kMixerInputs);
 }
 
 // Test mixer with many inputs in mixed post-Stop() and post-Play() states.
-TEST_F(AudioRendererMixerTest, ManyInputMixedStopPlay) {
+TEST_P(AudioRendererMixerTestCase, ManyInputMixedStopPlay) {
   InitializeInputs(kMixerInputs);
 
   // Start() all inputs.
   for (size_t i = 0; i < mixer_inputs_.size(); ++i)
     mixer_inputs_[i]->Start();
 
   // Stop() all even numbered mixer inputs and Play() all odd numbered inputs
   // and ensure we get the right value.
   for (size_t i = 1; i < mixer_inputs_.size(); i += 2) {
     mixer_inputs_[i - 1]->Stop();
     mixer_inputs_[i]->Play();
   }
-  for (int i = 0; i < kMixerCycles; ++i) {
-    fake_callback_->NextFillValue();
-    ASSERT_TRUE(RenderAndValidateAudioData(
-        fake_callback_->fill_value() * std::max(
-            mixer_inputs_.size() / 2, static_cast<size_t>(1))));
-  }
+  ASSERT_TRUE(RenderAndValidateAudioData(std::max(
+      mixer_inputs_.size() / 2, static_cast<size_t>(1))));
 
   for (size_t i = 1; i < mixer_inputs_.size(); i += 2)
     mixer_inputs_[i]->Stop();
 }
 
-TEST_F(AudioRendererMixerTest, OnRenderError) {
-  std::vector< scoped_refptr<AudioRendererMixerInput> > mixer_inputs;
-  for (int i = 0; i < kMixerInputs; ++i) {
-    scoped_refptr<AudioRendererMixerInput> mixer_input(
-        new AudioRendererMixerInput(mixer_));
-    mixer_input->Initialize(audio_parameters_, fake_callback_.get());
-    mixer_input->SetVolume(1.0f);
-    mixer_input->Start();
-    mixer_inputs_.push_back(mixer_input);
+TEST_P(AudioRendererMixerTestCase, OnRenderError) {
+  InitializeInputs(kMixerInputs);
+  for (size_t i = 0; i < mixer_inputs_.size(); ++i) {
+    mixer_inputs_[i]->Start();
+    EXPECT_CALL(*fake_callbacks_[i], OnRenderError()).Times(1);
   }
 
-  EXPECT_CALL(*fake_callback_, OnRenderError()).Times(kMixerInputs);
-  sink_->SimulateRenderError();
-  for (int i = 0; i < kMixerInputs; ++i)
+  mixer_callback_->OnRenderError();
+  for (size_t i = 0; i < mixer_inputs_.size(); ++i)
     mixer_inputs_[i]->Stop();
 }
 
+INSTANTIATE_TEST_CASE_P(
+    AudioRendererMixerTest, AudioRendererMixerTestCase, testing::Values(
+        // No resampling.
+        std::tr1::make_tuple(44100, 44100, 0.000000477),
+
+        // Upsampling.
+        std::tr1::make_tuple(44100, 48000, 0.0329405),
+
+        // Downsampling.
+        std::tr1::make_tuple(48000, 41000, 0.0410239)));
+
 }  // namespace media