Send data from mixer to APM limiter more often.
Before this change, the APM limiter used in FrameCombiner (a
sub-component of AudioMixer) only gets to process the data when the
number of non-muted streams is >1. If this number varies between <=1
and >1, the limiter's view of the data will have gaps during the
periods with <= 1 active stream.
This leads to discontinuities in the applied gain. These
discontinuities cause clicks in the output audio. This change
activates APM limiter processing based on the number of audio streams,
independently of their mutedness status.
BUG=chromium:695993
Review-Url: https://codereview.webrtc.org/2776113002
Cr-Commit-Position: refs/heads/master@{#17442}
diff --git a/webrtc/modules/audio_mixer/BUILD.gn b/webrtc/modules/audio_mixer/BUILD.gn
index 5075533..b38769c 100644
--- a/webrtc/modules/audio_mixer/BUILD.gn
+++ b/webrtc/modules/audio_mixer/BUILD.gn
@@ -70,11 +70,16 @@
"audio_frame_manipulator_unittest.cc",
"audio_mixer_impl_unittest.cc",
"frame_combiner_unittest.cc",
+ "gain_change_calculator.cc",
+ "gain_change_calculator.h",
+ "sine_wave_generator.cc",
+ "sine_wave_generator.h",
]
deps = [
":audio_frame_manipulator",
":audio_mixer_impl",
"../../api:audio_mixer_api",
+ "../../audio/utility:audio_frame_operations",
"../../base:rtc_base",
"../../base:rtc_base_approved",
"../../test:test_support",
diff --git a/webrtc/modules/audio_mixer/audio_mixer_impl.cc b/webrtc/modules/audio_mixer/audio_mixer_impl.cc
index d9e1951..7728c1c 100644
--- a/webrtc/modules/audio_mixer/audio_mixer_impl.cc
+++ b/webrtc/modules/audio_mixer/audio_mixer_impl.cc
@@ -141,8 +141,10 @@
{
rtc::CritScope lock(&crit_);
+ const size_t number_of_streams = audio_source_list_.size();
frame_combiner_.Combine(GetAudioFromSources(), number_of_channels,
- OutputFrequency(), audio_frame_for_mixing);
+ OutputFrequency(), number_of_streams,
+ audio_frame_for_mixing);
}
return;
diff --git a/webrtc/modules/audio_mixer/frame_combiner.cc b/webrtc/modules/audio_mixer/frame_combiner.cc
index d08ed0f..e47f8e7 100644
--- a/webrtc/modules/audio_mixer/frame_combiner.cc
+++ b/webrtc/modules/audio_mixer/frame_combiner.cc
@@ -16,6 +16,8 @@
#include <memory>
#include "webrtc/audio/utility/audio_frame_operations.h"
+#include "webrtc/base/array_view.h"
+#include "webrtc/base/checks.h"
#include "webrtc/base/logging.h"
#include "webrtc/modules/audio_mixer/audio_frame_manipulator.h"
#include "webrtc/modules/audio_mixer/audio_mixer_impl.h"
@@ -26,12 +28,25 @@
// Stereo, 48 kHz, 10 ms.
constexpr int kMaximalFrameSize = 2 * 48 * 10;
-void CombineZeroFrames(AudioFrame* audio_frame_for_mixing) {
+void CombineZeroFrames(bool use_limiter,
+ AudioProcessing* limiter,
+ AudioFrame* audio_frame_for_mixing) {
audio_frame_for_mixing->elapsed_time_ms_ = -1;
AudioFrameOperations::Mute(audio_frame_for_mixing);
+ // The limiter should still process a zero frame to avoid jumps in
+ // its gain curve.
+ if (use_limiter) {
+ RTC_DCHECK(limiter);
+ // The limiter smoothly increases frames with half gain to full
+ // volume. Here there's no need to apply half gain, since the frame
+ // is zero anyway.
+ limiter->ProcessStream(audio_frame_for_mixing);
+ }
}
void CombineOneFrame(const AudioFrame* input_frame,
+ bool use_limiter,
+ AudioProcessing* limiter,
AudioFrame* audio_frame_for_mixing) {
audio_frame_for_mixing->timestamp_ = input_frame->timestamp_;
audio_frame_for_mixing->elapsed_time_ms_ = input_frame->elapsed_time_ms_;
@@ -39,6 +54,82 @@
input_frame->data_ +
input_frame->num_channels_ * input_frame->samples_per_channel_,
audio_frame_for_mixing->data_);
+ if (use_limiter) {
+ AudioFrameOperations::ApplyHalfGain(audio_frame_for_mixing);
+ RTC_DCHECK(limiter);
+ limiter->ProcessStream(audio_frame_for_mixing);
+ AudioFrameOperations::Add(*audio_frame_for_mixing, audio_frame_for_mixing);
+ }
+}
+
+// Lower-level helper function called from Combine(...) when there
+// are several input frames.
+//
+// TODO(aleloi): change interface to ArrayView<int16_t> output_frame
+// once we have gotten rid of the APM limiter.
+//
+// Only the 'data' field of output_frame should be modified. The
+// rest are used for potentially sending the output to the APM
+// limiter.
+void CombineMultipleFrames(
+ const std::vector<rtc::ArrayView<const int16_t>>& input_frames,
+ bool use_limiter,
+ AudioProcessing* limiter,
+ AudioFrame* audio_frame_for_mixing) {
+ RTC_DCHECK(!input_frames.empty());
+ RTC_DCHECK(audio_frame_for_mixing);
+
+ const size_t frame_length = input_frames.front().size();
+ for (const auto& frame : input_frames) {
+ RTC_DCHECK_EQ(frame_length, frame.size());
+ }
+
+ // Algorithm: int16 frames are added to a sufficiently large
+ // statically allocated int32 buffer. For > 2 participants this is
+ // more efficient than addition in place in the int16 audio
+ // frame. The audio quality loss due to halving the samples is
+ // smaller than 16-bit addition in place.
+ RTC_DCHECK_GE(kMaximalFrameSize, frame_length);
+ std::array<int32_t, kMaximalFrameSize> add_buffer;
+
+ add_buffer.fill(0);
+
+ for (const auto& frame : input_frames) {
+ std::transform(frame.begin(), frame.end(), add_buffer.begin(),
+ add_buffer.begin(), std::plus<int32_t>());
+ }
+
+ if (use_limiter) {
+ // Halve all samples to avoid saturation before limiting.
+ std::transform(add_buffer.begin(), add_buffer.begin() + frame_length,
+ audio_frame_for_mixing->data_, [](int32_t a) {
+ return rtc::saturated_cast<int16_t>(a / 2);
+ });
+
+ // Smoothly limit the audio.
+ RTC_DCHECK(limiter);
+ const int error = limiter->ProcessStream(audio_frame_for_mixing);
+ if (error != limiter->kNoError) {
+ LOG_F(LS_ERROR) << "Error from AudioProcessing: " << error;
+ RTC_NOTREACHED();
+ }
+
+ // And now we can safely restore the level. This procedure results in
+ // some loss of resolution, deemed acceptable.
+ //
+ // It's possible to apply the gain in the AGC (with a target level of 0 dbFS
+ // and compression gain of 6 dB). However, in the transition frame when this
+ // is enabled (moving from one to two audio sources) it has the potential to
+ // create discontinuities in the mixed frame.
+ //
+ // Instead we double the frame (with addition since left-shifting a
+ // negative value is undefined).
+ AudioFrameOperations::Add(*audio_frame_for_mixing, audio_frame_for_mixing);
+ } else {
+ std::transform(add_buffer.begin(), add_buffer.begin() + frame_length,
+ audio_frame_for_mixing->data_,
+ [](int32_t a) { return rtc::saturated_cast<int16_t>(a); });
+ }
}
std::unique_ptr<AudioProcessing> CreateLimiter() {
@@ -74,6 +165,7 @@
void FrameCombiner::Combine(const std::vector<AudioFrame*>& mix_list,
size_t number_of_channels,
int sample_rate,
+ size_t number_of_streams,
AudioFrame* audio_frame_for_mixing) const {
RTC_DCHECK(audio_frame_for_mixing);
const size_t samples_per_channel = static_cast<size_t>(
@@ -97,76 +189,22 @@
-1, 0, nullptr, samples_per_channel, sample_rate, AudioFrame::kUndefined,
AudioFrame::kVadUnknown, number_of_channels);
+ const bool use_limiter_this_round = use_apm_limiter_ && number_of_streams > 1;
+
if (mix_list.empty()) {
- CombineZeroFrames(audio_frame_for_mixing);
+ CombineZeroFrames(use_limiter_this_round, limiter_.get(),
+ audio_frame_for_mixing);
} else if (mix_list.size() == 1) {
- CombineOneFrame(mix_list.front(), audio_frame_for_mixing);
+ CombineOneFrame(mix_list.front(), use_limiter_this_round, limiter_.get(),
+ audio_frame_for_mixing);
} else {
std::vector<rtc::ArrayView<const int16_t>> input_frames;
for (size_t i = 0; i < mix_list.size(); ++i) {
input_frames.push_back(rtc::ArrayView<const int16_t>(
mix_list[i]->data_, samples_per_channel * number_of_channels));
}
- CombineMultipleFrames(input_frames, audio_frame_for_mixing);
- }
-}
-
-void FrameCombiner::CombineMultipleFrames(
- const std::vector<rtc::ArrayView<const int16_t>>& input_frames,
- AudioFrame* audio_frame_for_mixing) const {
- RTC_DCHECK(!input_frames.empty());
- RTC_DCHECK(audio_frame_for_mixing);
-
- const size_t frame_length = input_frames.front().size();
- for (const auto& frame : input_frames) {
- RTC_DCHECK_EQ(frame_length, frame.size());
- }
-
- // Algorithm: int16 frames are added to a sufficiently large
- // statically allocated int32 buffer. For > 2 participants this is
- // more efficient than addition in place in the int16 audio
- // frame. The audio quality loss due to halving the samples is
- // smaller than 16-bit addition in place.
- RTC_DCHECK_GE(kMaximalFrameSize, frame_length);
- std::array<int32_t, kMaximalFrameSize> add_buffer;
-
- add_buffer.fill(0);
-
- for (const auto& frame : input_frames) {
- std::transform(frame.begin(), frame.end(), add_buffer.begin(),
- add_buffer.begin(), std::plus<int32_t>());
- }
-
- if (use_apm_limiter_) {
- // Halve all samples to avoid saturation before limiting.
- std::transform(add_buffer.begin(), add_buffer.begin() + frame_length,
- audio_frame_for_mixing->data_, [](int32_t a) {
- return rtc::saturated_cast<int16_t>(a / 2);
- });
-
- // Smoothly limit the audio.
- RTC_DCHECK(limiter_);
- const int error = limiter_->ProcessStream(audio_frame_for_mixing);
- if (error != limiter_->kNoError) {
- LOG_F(LS_ERROR) << "Error from AudioProcessing: " << error;
- RTC_NOTREACHED();
- }
-
- // And now we can safely restore the level. This procedure results in
- // some loss of resolution, deemed acceptable.
- //
- // It's possible to apply the gain in the AGC (with a target level of 0 dbFS
- // and compression gain of 6 dB). However, in the transition frame when this
- // is enabled (moving from one to two audio sources) it has the potential to
- // create discontinuities in the mixed frame.
- //
- // Instead we double the frame (with addition since left-shifting a
- // negative value is undefined).
- AudioFrameOperations::Add(*audio_frame_for_mixing, audio_frame_for_mixing);
- } else {
- std::transform(add_buffer.begin(), add_buffer.begin() + frame_length,
- audio_frame_for_mixing->data_,
- [](int32_t a) { return rtc::saturated_cast<int16_t>(a); });
+ CombineMultipleFrames(input_frames, use_limiter_this_round, limiter_.get(),
+ audio_frame_for_mixing);
}
}
} // namespace webrtc
diff --git a/webrtc/modules/audio_mixer/frame_combiner.h b/webrtc/modules/audio_mixer/frame_combiner.h
index 11c2e68..7b7e240 100644
--- a/webrtc/modules/audio_mixer/frame_combiner.h
+++ b/webrtc/modules/audio_mixer/frame_combiner.h
@@ -26,26 +26,17 @@
// Combine several frames into one. Assumes sample_rate,
// samples_per_channel of the input frames match the parameters. The
- // extra parameters are needed because 'mix_list' can be empty.
+ // parameters 'number_of_channels' and 'sample_rate' are needed
+ // because 'mix_list' can be empty. The parameter
+ // 'number_of_streams' is used for determining whether to pass the
+ // data through a limiter.
void Combine(const std::vector<AudioFrame*>& mix_list,
size_t number_of_channels,
int sample_rate,
+ size_t number_of_streams,
AudioFrame* audio_frame_for_mixing) const;
private:
- // Lower-level helper function called from Combine(...) when there
- // are several input frames.
- //
- // TODO(aleloi): change interface to ArrayView<int16_t> output_frame
- // once we have gotten rid of the APM limiter.
- //
- // Only the 'data' field of output_frame should be modified. The
- // rest are used for potentially sending the output to the APM
- // limiter.
- void CombineMultipleFrames(
- const std::vector<rtc::ArrayView<const int16_t>>& input_frames,
- AudioFrame* audio_frame_for_mixing) const;
-
const bool use_apm_limiter_;
std::unique_ptr<AudioProcessing> limiter_;
};
diff --git a/webrtc/modules/audio_mixer/frame_combiner_unittest.cc b/webrtc/modules/audio_mixer/frame_combiner_unittest.cc
index 13c6601..8d745f6 100644
--- a/webrtc/modules/audio_mixer/frame_combiner_unittest.cc
+++ b/webrtc/modules/audio_mixer/frame_combiner_unittest.cc
@@ -14,7 +14,10 @@
#include <sstream>
#include <string>
+#include "webrtc/audio/utility/audio_frame_operations.h"
#include "webrtc/base/checks.h"
+#include "webrtc/modules/audio_mixer/gain_change_calculator.h"
+#include "webrtc/modules/audio_mixer/sine_wave_generator.h"
#include "webrtc/test/gtest.h"
namespace webrtc {
@@ -24,9 +27,23 @@
int number_of_channels,
int number_of_sources) {
std::ostringstream ss;
- ss << "Sample rate: " << sample_rate_hz << " ";
- ss << "Number of channels: " << number_of_channels << " ";
- ss << "Number of sources: " << number_of_sources;
+ ss << "Sample rate: " << sample_rate_hz << " ,";
+ ss << "number of channels: " << number_of_channels << " ,";
+ ss << "number of sources: " << number_of_sources;
+ return ss.str();
+}
+
+std::string ProduceDebugText(int sample_rate_hz,
+ int number_of_channels,
+ int number_of_sources,
+ bool limiter_active,
+ float wave_frequency) {
+ std::ostringstream ss;
+ ss << "Sample rate: " << sample_rate_hz << " ,";
+ ss << "number of channels: " << number_of_channels << " ,";
+ ss << "number of sources: " << number_of_sources << " ,";
+ ss << "limiter active: " << (limiter_active ? "true" : "false") << " ,";
+ ss << "wave frequency: " << wave_frequency << " ,";
return ss.str();
}
@@ -57,7 +74,7 @@
const std::vector<AudioFrame*> frames_to_combine(
all_frames.begin(), all_frames.begin() + number_of_frames);
combiner.Combine(frames_to_combine, number_of_channels, rate,
- &audio_frame_for_mixing);
+ frames_to_combine.size(), &audio_frame_for_mixing);
}
}
}
@@ -79,7 +96,7 @@
const std::vector<AudioFrame*> frames_to_combine(
all_frames.begin(), all_frames.begin() + number_of_frames);
combiner.Combine(frames_to_combine, number_of_channels, rate,
- &audio_frame_for_mixing);
+ frames_to_combine.size(), &audio_frame_for_mixing);
}
}
}
@@ -93,7 +110,7 @@
const std::vector<AudioFrame*> frames_to_combine;
combiner.Combine(frames_to_combine, number_of_channels, rate,
- &audio_frame_for_mixing);
+ frames_to_combine.size(), &audio_frame_for_mixing);
const std::vector<int16_t> mixed_data(
audio_frame_for_mixing.data_,
@@ -116,7 +133,7 @@
0);
const std::vector<AudioFrame*> frames_to_combine = {&frame1};
combiner.Combine(frames_to_combine, number_of_channels, rate,
- &audio_frame_for_mixing);
+ frames_to_combine.size(), &audio_frame_for_mixing);
const std::vector<int16_t> mixed_data(
audio_frame_for_mixing.data_,
@@ -129,4 +146,57 @@
}
}
+// Send a sine wave through the FrameCombiner, and check that the
+// difference between input and output varies smoothly. This is to
+// catch issues like chromium:695993.
+TEST(FrameCombiner, GainCurveIsSmoothForAlternatingNumberOfStreams) {
+ // Test doesn't work with rates requiring a band split, because it
+ // introduces a small delay measured in single samples, and this
+ // test cannot handle it.
+ //
+ // TODO(aleloi): Add more rates when APM limiter doesn't use band
+ // split.
+ for (const bool use_limiter : {true, false}) {
+ for (const int rate : {8000, 16000}) {
+ constexpr int number_of_channels = 2;
+ for (const float wave_frequency : {50, 400, 3200}) {
+ SCOPED_TRACE(ProduceDebugText(rate, number_of_channels, 1, use_limiter,
+ wave_frequency));
+
+ FrameCombiner combiner(use_limiter);
+
+ constexpr int16_t wave_amplitude = 30000;
+ SineWaveGenerator wave_generator(wave_frequency, wave_amplitude);
+
+ GainChangeCalculator change_calculator;
+ float cumulative_change = 0.f;
+
+ constexpr size_t iterations = 100;
+
+ for (size_t i = 0; i < iterations; ++i) {
+ SetUpFrames(rate, number_of_channels);
+ wave_generator.GenerateNextFrame(&frame1);
+ AudioFrameOperations::Mute(&frame2);
+
+ std::vector<AudioFrame*> frames_to_combine = {&frame1};
+ if (i % 2 == 0) {
+ frames_to_combine.push_back(&frame2);
+ }
+ const size_t number_of_samples =
+ frame1.samples_per_channel_ * number_of_channels;
+
+ // Ensures limiter is on if 'use_limiter'.
+ constexpr size_t number_of_streams = 2;
+ combiner.Combine(frames_to_combine, number_of_channels, rate,
+ number_of_streams, &audio_frame_for_mixing);
+ cumulative_change += change_calculator.CalculateGainChange(
+ rtc::ArrayView<const int16_t>(frame1.data_, number_of_samples),
+ rtc::ArrayView<const int16_t>(audio_frame_for_mixing.data_,
+ number_of_samples));
+ }
+ RTC_DCHECK_LT(cumulative_change, 10);
+ }
+ }
+ }
+}
} // namespace webrtc
diff --git a/webrtc/modules/audio_mixer/gain_change_calculator.cc b/webrtc/modules/audio_mixer/gain_change_calculator.cc
new file mode 100644
index 0000000..13017d4
--- /dev/null
+++ b/webrtc/modules/audio_mixer/gain_change_calculator.cc
@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+ *
+ * Use of this source code is governed by a BSD-style license
+ * that can be found in the LICENSE file in the root of the source
+ * tree. An additional intellectual property rights grant can be found
+ * in the file PATENTS. All contributing project authors may
+ * be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/modules/audio_mixer/gain_change_calculator.h"
+
+#include <math.h>
+#include <vector>
+
+namespace webrtc {
+
+namespace {
+constexpr int16_t kReliabilityThreshold = 100;
+} // namespace
+
+float GainChangeCalculator::CalculateGainChange(
+ rtc::ArrayView<const int16_t> in,
+ rtc::ArrayView<const int16_t> out) {
+ RTC_DCHECK_EQ(in.size(), out.size());
+
+ std::vector<float> gain(in.size());
+ CalculateGain(in, out, gain);
+ return CalculateDifferences(gain);
+}
+
+void GainChangeCalculator::CalculateGain(rtc::ArrayView<const int16_t> in,
+ rtc::ArrayView<const int16_t> out,
+ rtc::ArrayView<float> gain) {
+ RTC_DCHECK_EQ(in.size(), out.size());
+ RTC_DCHECK_EQ(in.size(), gain.size());
+
+ for (size_t i = 0; i < in.size(); ++i) {
+ if (std::abs(in[i]) >= kReliabilityThreshold) {
+ last_reliable_gain_ = out[i] / static_cast<float>(in[i]);
+ }
+ gain[i] = last_reliable_gain_;
+ }
+}
+
+float GainChangeCalculator::CalculateDifferences(
+ rtc::ArrayView<const float> values) {
+ float res = 0;
+ for (float f : values) {
+ res += fabs(f - last_value_);
+ last_value_ = f;
+ }
+ return res;
+}
+} // namespace webrtc
diff --git a/webrtc/modules/audio_mixer/gain_change_calculator.h b/webrtc/modules/audio_mixer/gain_change_calculator.h
new file mode 100644
index 0000000..ca7bf03
--- /dev/null
+++ b/webrtc/modules/audio_mixer/gain_change_calculator.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+ *
+ * Use of this source code is governed by a BSD-style license
+ * that can be found in the LICENSE file in the root of the source
+ * tree. An additional intellectual property rights grant can be found
+ * in the file PATENTS. All contributing project authors may
+ * be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_MIXER_GAIN_CHANGE_CALCULATOR_H_
+#define WEBRTC_MODULES_AUDIO_MIXER_GAIN_CHANGE_CALCULATOR_H_
+
+#include "webrtc/base/array_view.h"
+
+namespace webrtc {
+
+class GainChangeCalculator {
+ public:
+ // The 'out' signal is assumed to be produced from 'in' by applying
+ // a smoothly varying gain. This method computes variations of the
+ // gain and handles special cases when the samples are small.
+ float CalculateGainChange(rtc::ArrayView<const int16_t> in,
+ rtc::ArrayView<const int16_t> out);
+
+ private:
+ void CalculateGain(rtc::ArrayView<const int16_t> in,
+ rtc::ArrayView<const int16_t> out,
+ rtc::ArrayView<float> gain);
+
+ float CalculateDifferences(rtc::ArrayView<const float> values);
+ float last_value_ = 0.f;
+ float last_reliable_gain_ = 1.0f;
+};
+
+} // namespace webrtc
+
+#endif // WEBRTC_MODULES_AUDIO_MIXER_GAIN_CHANGE_CALCULATOR_H_
diff --git a/webrtc/modules/audio_mixer/sine_wave_generator.cc b/webrtc/modules/audio_mixer/sine_wave_generator.cc
new file mode 100644
index 0000000..f16312f
--- /dev/null
+++ b/webrtc/modules/audio_mixer/sine_wave_generator.cc
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+ *
+ * Use of this source code is governed by a BSD-style license
+ * that can be found in the LICENSE file in the root of the source
+ * tree. An additional intellectual property rights grant can be found
+ * in the file PATENTS. All contributing project authors may
+ * be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/modules/audio_mixer/sine_wave_generator.h"
+
+#include <math.h>
+
+#include "webrtc/base/safe_conversions.h"
+
+namespace webrtc {
+
+namespace {
+constexpr float kPi = 3.14159265f;
+} // namespace
+
+void SineWaveGenerator::GenerateNextFrame(AudioFrame* frame) {
+ RTC_DCHECK(frame);
+ for (size_t i = 0; i < frame->samples_per_channel_; ++i) {
+ for (size_t ch = 0; ch < frame->num_channels_; ++ch) {
+ frame->data_[frame->num_channels_ * i + ch] =
+ rtc::saturated_cast<int16_t>(amplitude_ * sinf(phase_));
+ }
+ phase_ += wave_frequency_hz_ * 2 * kPi / frame->sample_rate_hz_;
+ }
+}
+} // namespace webrtc
diff --git a/webrtc/modules/audio_mixer/sine_wave_generator.h b/webrtc/modules/audio_mixer/sine_wave_generator.h
new file mode 100644
index 0000000..7d17293
--- /dev/null
+++ b/webrtc/modules/audio_mixer/sine_wave_generator.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+ *
+ * Use of this source code is governed by a BSD-style license
+ * that can be found in the LICENSE file in the root of the source
+ * tree. An additional intellectual property rights grant can be found
+ * in the file PATENTS. All contributing project authors may
+ * be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_MIXER_SINE_WAVE_GENERATOR_H_
+#define WEBRTC_MODULES_AUDIO_MIXER_SINE_WAVE_GENERATOR_H_
+
+#include "webrtc/base/checks.h"
+#include "webrtc/modules/include/module_common_types.h"
+
+namespace webrtc {
+
+class SineWaveGenerator {
+ public:
+ SineWaveGenerator(float wave_frequency_hz, int16_t amplitude)
+ : wave_frequency_hz_(wave_frequency_hz), amplitude_(amplitude) {
+ RTC_DCHECK_GT(wave_frequency_hz, 0);
+ }
+
+ // Produces appropriate output based on frame->num_channels_,
+ // frame->sample_rate_hz_.
+ void GenerateNextFrame(AudioFrame* frame);
+
+ private:
+ float phase_ = 0.f;
+ const float wave_frequency_hz_;
+ const int16_t amplitude_;
+};
+
+} // namespace webrtc
+
+#endif // WEBRTC_MODULES_AUDIO_MIXER_SINE_WAVE_GENERATOR_H_