AudioCommon: extract AudioStretcher class for time-stretching

1 files changed, 4 insertions, 67 deletions

diff --git a/Source/Core/AudioCommon/Mixer.cpp b/Source/Core/AudioCommon/Mixer.cpp
index 2454042fe2..8d4ef3bc81 100644
--- a/Source/Core/AudioCommon/Mixer.cpp
+++ b/Source/Core/AudioCommon/Mixer.cpp
@@ -14,19 +14,10 @@
 #include "Common/Swap.h"
 #include "Core/ConfigManager.h"
 
-CMixer::CMixer(unsigned int BackendSampleRate) : m_sampleRate(BackendSampleRate)
+CMixer::CMixer(unsigned int BackendSampleRate)
+    : m_sampleRate(BackendSampleRate), m_stretcher(BackendSampleRate)
 {
   INFO_LOG(AUDIO_INTERFACE, "Mixer is initialized");
-
-  m_sound_touch.setChannels(2);
-  m_sound_touch.setSampleRate(BackendSampleRate);
-  m_sound_touch.setPitch(1.0);
-  m_sound_touch.setTempo(1.0);
-  m_sound_touch.setSetting(SETTING_USE_QUICKSEEK, 0);
-  m_sound_touch.setSetting(SETTING_SEQUENCE_MS, 62);
-  m_sound_touch.setSetting(SETTING_SEEKWINDOW_MS, 28);
-  m_sound_touch.setSetting(SETTING_OVERLAP_MS, 8);
-
   DPL2Reset();
 }
 
@@ -146,10 +137,10 @@ unsigned int CMixer::Mix(short* samples, unsigned int num_samples)
 
     if (!m_is_stretching)
     {
-      m_sound_touch.clear();
+      m_stretcher.Clear();
       m_is_stretching = true;
     }
-    StretchAudio(m_stretch_buffer.data(), available_samples, samples, num_samples);
+    m_stretcher.StretchAudio(m_stretch_buffer.data(), available_samples, samples, num_samples);
   }
   else
   {
@@ -181,60 +172,6 @@ unsigned int CMixer::MixSurround(float* samples, unsigned int num_samples)
   return available_samples;
 }
 
-void CMixer::StretchAudio(const short* in, unsigned int num_in, short* out, unsigned int num_out)
-{
-  const double time_delta = static_cast<double>(num_out) / m_sampleRate;  // seconds
-
-  // We were given actual_samples number of samples, and num_samples were requested from us.
-  double current_ratio = static_cast<double>(num_in) / static_cast<double>(num_out);
-
-  const double max_latency = SConfig::GetInstance().m_audio_stretch_max_latency;
-  const double max_backlog = m_sampleRate * max_latency / 1000.0 / m_stretch_ratio;
-  const double backlog_fullness = m_sound_touch.numSamples() / max_backlog;
-  if (backlog_fullness > 5.0)
-  {
-    // Too many samples in backlog: Don't push anymore on
-    num_in = 0;
-  }
-
-  // We ideally want the backlog to be about 50% full.
-  // This gives some headroom both ways to prevent underflow and overflow.
-  // We tweak current_ratio to encourage this.
-  constexpr double tweak_time_scale = 0.5;  // seconds
-  current_ratio *= 1.0 + 2.0 * (backlog_fullness - 0.5) * (time_delta / tweak_time_scale);
-
-  // This low-pass filter smoothes out variance in the calculated stretch ratio.
-  // The time-scale determines how responsive this filter is.
-  constexpr double lpf_time_scale = 1.0;  // seconds
-  const double m_lpf_gain = 1.0 - std::exp(-time_delta / lpf_time_scale);
-  m_stretch_ratio += m_lpf_gain * (current_ratio - m_stretch_ratio);
-
-  // Place a lower limit of 10% speed.  When a game boots up, there will be
-  // many silence samples.  These do not need to be timestretched.
-  m_stretch_ratio = std::max(m_stretch_ratio, 0.1);
-  m_sound_touch.setTempo(m_stretch_ratio);
-
-  DEBUG_LOG(AUDIO, "Audio stretching: samples:%u/%u ratio:%f backlog:%f gain: %f", num_in, num_out,
-            m_stretch_ratio, backlog_fullness, m_lpf_gain);
-
-  m_sound_touch.putSamples(in, num_in);
-
-  const size_t samples_received = m_sound_touch.receiveSamples(out, num_out);
-
-  if (samples_received != 0)
-  {
-    m_last_stretched_sample[0] = out[samples_received * 2 - 2];
-    m_last_stretched_sample[1] = out[samples_received * 2 - 1];
-  }
-
-  // Preform padding if we've run out of samples.
-  for (size_t i = samples_received; i < num_out; i++)
-  {
-    out[i * 2 + 0] = m_last_stretched_sample[0];
-    out[i * 2 + 1] = m_last_stretched_sample[1];
-  }
-}
-
 void CMixer::MixerFifo::PushSamples(const short* samples, unsigned int num_samples)
 {
   // Cache access in non-volatile variable