AudioCore: Implement time stretcher (#1737)

* AudioCore: Implement time stretcher

* fixup! AudioCore: Implement time stretcher

* fixup! fixup! AudioCore: Implement time stretcher

* fixup! fixup! fixup! AudioCore: Implement time stretcher

* fixup! fixup! fixup! fixup! AudioCore: Implement time stretcher

* fixup! fixup! fixup! fixup! fixup! AudioCore: Implement time stretcher

1 files changed, 144 insertions, 0 deletions

diff --git a/src/audio_core/time_stretch.cpp b/src/audio_core/time_stretch.cpp
new file mode 100644
index 000000000..ea38f40d0
--- /dev/null
+++ b/src/audio_core/time_stretch.cpp
@@ -0,0 +1,144 @@
+// Copyright 2016 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <chrono>
+#include <cmath>
+#include <vector>
+
+#include <SoundTouch.h>
+
+#include "audio_core/audio_core.h"
+#include "audio_core/time_stretch.h"
+
+#include "common/common_types.h"
+#include "common/logging/log.h"
+#include "common/math_util.h"
+
+using steady_clock = std::chrono::steady_clock;
+
+namespace AudioCore {
+
+constexpr double MIN_RATIO = 0.1;
+constexpr double MAX_RATIO = 100.0;
+
+static double ClampRatio(double ratio) {
+    return MathUtil::Clamp(ratio, MIN_RATIO, MAX_RATIO);
+}
+
+constexpr double MIN_DELAY_TIME = 0.05; // Units: seconds
+constexpr double MAX_DELAY_TIME = 0.25; // Units: seconds
+constexpr size_t DROP_FRAMES_SAMPLE_DELAY = 16000; // Units: samples
+
+constexpr double SMOOTHING_FACTOR = 0.007;
+
+struct TimeStretcher::Impl {
+    soundtouch::SoundTouch soundtouch;
+
+    steady_clock::time_point frame_timer = steady_clock::now();
+    size_t samples_queued = 0;
+
+    double smoothed_ratio = 1.0;
+
+    double sample_rate = static_cast<double>(native_sample_rate);
+};
+
+std::vector<s16> TimeStretcher::Process(size_t samples_in_queue) {
+    // This is a very simple algorithm without any fancy control theory. It works and is stable.
+
+    double ratio = CalculateCurrentRatio();
+    ratio = CorrectForUnderAndOverflow(ratio, samples_in_queue);
+    impl->smoothed_ratio = (1.0 - SMOOTHING_FACTOR) * impl->smoothed_ratio + SMOOTHING_FACTOR * ratio;
+    impl->smoothed_ratio = ClampRatio(impl->smoothed_ratio);
+
+    // SoundTouch's tempo definition the inverse of our ratio definition.
+    impl->soundtouch.setTempo(1.0 / impl->smoothed_ratio);
+
+    std::vector<s16> samples = GetSamples();
+    if (samples_in_queue >= DROP_FRAMES_SAMPLE_DELAY) {
+        samples.clear();
+        LOG_DEBUG(Audio, "Dropping frames!");
+    }
+    return samples;
+}
+
+TimeStretcher::TimeStretcher() : impl(std::make_unique<Impl>()) {
+    impl->soundtouch.setPitch(1.0);
+    impl->soundtouch.setChannels(2);
+    impl->soundtouch.setSampleRate(native_sample_rate);
+    Reset();
+}
+
+TimeStretcher::~TimeStretcher() {
+    impl->soundtouch.clear();
+}
+
+void TimeStretcher::SetOutputSampleRate(unsigned int sample_rate) {
+    impl->sample_rate = static_cast<double>(sample_rate);
+    impl->soundtouch.setRate(static_cast<double>(native_sample_rate) / impl->sample_rate);
+}
+
+void TimeStretcher::AddSamples(const s16* buffer, size_t num_samples) {
+    impl->soundtouch.putSamples(buffer, static_cast<uint>(num_samples));
+    impl->samples_queued += num_samples;
+}
+
+void TimeStretcher::Flush() {
+    impl->soundtouch.flush();
+}
+
+void TimeStretcher::Reset() {
+    impl->soundtouch.setTempo(1.0);
+    impl->soundtouch.clear();
+    impl->smoothed_ratio = 1.0;
+    impl->frame_timer = steady_clock::now();
+    impl->samples_queued = 0;
+    SetOutputSampleRate(native_sample_rate);
+}
+
+double TimeStretcher::CalculateCurrentRatio() {
+    const steady_clock::time_point now = steady_clock::now();
+    const std::chrono::duration<double> duration = now - impl->frame_timer;
+
+    const double expected_time = static_cast<double>(impl->samples_queued) / static_cast<double>(native_sample_rate);
+    const double actual_time = duration.count();
+
+    double ratio;
+    if (expected_time != 0) {
+        ratio = ClampRatio(actual_time / expected_time);
+    } else {
+        ratio = impl->smoothed_ratio;
+    }
+
+    impl->frame_timer = now;
+    impl->samples_queued = 0;
+
+    return ratio;
+}
+
+double TimeStretcher::CorrectForUnderAndOverflow(double ratio, size_t sample_delay) const {
+    const size_t min_sample_delay = static_cast<size_t>(MIN_DELAY_TIME * impl->sample_rate);
+    const size_t max_sample_delay = static_cast<size_t>(MAX_DELAY_TIME * impl->sample_rate);
+
+    if (sample_delay < min_sample_delay) {
+        // Make the ratio bigger.
+        ratio = ratio > 1.0 ? ratio * ratio : sqrt(ratio);
+    } else if (sample_delay > max_sample_delay) {
+        // Make the ratio smaller.
+        ratio = ratio > 1.0 ? sqrt(ratio) : ratio * ratio;
+    }
+
+    return ClampRatio(ratio);
+}
+
+std::vector<s16> TimeStretcher::GetSamples() {
+    uint available = impl->soundtouch.numSamples();
+
+    std::vector<s16> output(static_cast<size_t>(available) * 2);
+
+    impl->soundtouch.receiveSamples(output.data(), available);
+
+    return output;
+}
+
+} // namespace AudioCore