fixup: use stretcher properly, play silence on glitches

app/src/main/cpp/PlaybackEngine.cpp

@@ -273,9 +273,15 @@ void PlaybackEngine::musicFeedThread() {
         }
 
         if(haveTimeRatio.load() || haveStretchFactor.load()) {
+            LOGI("ratio: %.3lf stretch: %.3lf", timeRatio.load(), stretchFactor.load());
+#if 1
             double ratio = timeRatio.load() * stretchFactor.load();
+#else
+            double ratio = timeRatio.load();
+#endif
             stretcher.setTimeRatio(ratio);
-            stretcher.setPitchScale(1.0 / ratio);
+            //stretcher.setPitchScale(1.0 / ratio);
+            stretcher.setPitchScale(1.0 / timeRatio.load());
             haveTimeRatio.store(false);
             haveStretchFactor.store(false);
         }
@@ -622,6 +628,11 @@ void MusicProvider::onAudioReady(float *data, int32_t frames) {
         // this is an audio glitch
         // TODO: bubble info upwards, in a counter (so we can collect device-specific glitch stats)
         LOGI("stretcher lag: %d requested, %d available", num_frames_requested, num_frames_available);
+        if(num_frames_available == 0) {
+            // at least play silence, avoiding to play garbled stuff
+            memset(data, 0, sizeof(float)*frames*num_ch_out);
+            return;
+        }
     }
     size_t num_frames = std::min(num_frames_available, num_frames_requested);
     stretcher->retrieve(buf_ptr, num_frames);

app/src/main/cpp/TempoController.cpp

@@ -8,7 +8,9 @@ TempoController::TempoController(std::atomic<bool> *have_stretch_factor, std::at
     have_stretch_factor(have_stretch_factor),
     stretch_factor(stretch_factor),
     lastBeatT(0.0),
-    lastStepT(0.0)
+    lastStepT(0.0),
+    dtBeat(0.0),
+    dtStep(0.0)
 {
     this->have_stretch_factor->store(false);
     this->stretch_factor->store(1.0);
@@ -28,7 +30,6 @@ void TempoController::seekTo(double oldMarkerPosSec, double newMarkerPosSec) {
     std::lock_guard<std::mutex> lock(mMutex);
     double dt = newMarkerPosSec - oldMarkerPosSec;
     lastBeatT += dt;
-    lastStepT += dt;
 }
 
 /**
@@ -37,7 +38,9 @@ void TempoController::seekTo(double oldMarkerPosSec, double newMarkerPosSec) {
  */
 void TempoController::onBeat(double t) {
     std::lock_guard<std::mutex> lock(mMutex);
+    if(lastBeatT != 0.0) dtBeat = t - lastBeatT;
     lastBeatT = t;
+    setStretchFactor();
 }
 
 /**
@@ -46,5 +49,16 @@ void TempoController::onBeat(double t) {
  */
 void TempoController::onStep(double t) {
     std::lock_guard<std::mutex> lock(mMutex);
+    if(lastStepT != 0.0) dtStep = t - lastStepT;
     lastStepT = t;
+    //setStretchFactor();  // one call is enough. otherwise we set twice roughly around the same time.
+}
+
+void TempoController::setStretchFactor() {
+    if(dtBeat == 0.0 || dtStep == 0.0) return;
+    double ratio = dtStep / dtBeat;
+    ratio = std::min(3.3, ratio);
+    ratio = std::max(0.3, ratio);
+    this->have_stretch_factor->store(true);
+    this->stretch_factor->store(ratio);
 }

app/src/main/cpp/TempoController.h

@@ -17,6 +17,8 @@ private:
     std::atomic<double> *stretch_factor;
     double lastBeatT;
     double lastStepT;
+    double dtBeat;
+    double dtStep;
 public:
     TempoController(std::atomic<bool> *have_stretch_factor, std::atomic<double> *stretch_factor);
     void reset(std::vector<double> beatTimesSec);
@@ -33,6 +35,8 @@ public:
      * @param t marker position in sec of original music time
      */
     void onStep(double t);
+private:
+    void setStretchFactor();
 };
 
 #endif //LOCKSTEP_TEMPOCONTROLLER_H