feat: actually map channels

app/src/main/cpp/PlaybackEngine.h

@@ -18,7 +18,7 @@
 /** Provides music through a regular callback to oboe. Called from separate oboe thread. */
 class MusicProvider : public AudioCallbackProvider {
 public:
-    explicit MusicProvider(RubberBand::RubberBandStretcher *stretcher, size_t buf_size_samples);
+    explicit MusicProvider(RubberBand::RubberBandStretcher *stretcher, size_t buf_size_samples, int num_ch_out);
     ~MusicProvider() override;
 
     /** Called from separate oboe thread. */
@@ -26,8 +26,10 @@ public:
 private:
     RubberBand::RubberBandStretcher *stretcher;
     float *buf;
+    float **buf_ptr;
     int idebug;
     size_t buf_size_samples;
+    int num_ch_out;
 };
 
 class PlaybackEngine : public StepListener {
@@ -47,13 +49,17 @@ private:
     std::atomic<bool> exitMusicFeedThread;
     int android_fd;
     std::atomic<bool> haveTimeRatio;
-    double timeRatio;
-    int playbackRate;
+    std::atomic<double> timeRatio;
+    std::atomic<int> playbackRate;
+    std::atomic<int> numOutChannels;
+    std::atomic<int> numInChannels;
+    /** this is actually in frames, not samples */
     static size_t constexpr buf_size_samples = 1024;
     void initRubberBand();
     void closeRubberBand();
     void closeMusicFile();
     void musicFeedThread();
+    void mapChannels(int *channel_map, int num_ch_in, int num_ch_out);
 };
 
 #endif //LOCKSTEP_PLAYBACKENGINE_H