feat: play music through librubberband

app/src/main/cpp/PlaybackEngine.h

@@ -7,7 +7,28 @@
 
 #include "StepListener.h"
 #include "MixingPlayer.h"
+#include "RubberBandStretcher.h"
+#include "mp3file.h"
+#include "AudioCallback.h"
 #include <string>
+#include <thread>
+#include <memory>
+#include <atomic>
+
+/** Provides music through a regular callback to oboe. Called from separate oboe thread. */
+class MusicProvider : public AudioCallbackProvider {
+public:
+    explicit MusicProvider(RubberBand::RubberBandStretcher *stretcher);
+    ~MusicProvider() override;
+
+    /** Called from separate oboe thread. */
+    void onAudioReady(float *data, int32_t frames) override;
+private:
+    const size_t num_buf_samples = 48000;
+    RubberBand::RubberBandStretcher *stretcher;
+    float *buf;
+    int idebug;
+};
 
 class PlaybackEngine : public StepListener {
 public:
@@ -17,8 +38,18 @@ public:
     virtual void playBeat();
     void playMusic(int fd);
 private:
+    RubberBand::RubberBandStretcher stretcher;
     MixingPlayer *mPlayer;
     std::string mFilesDir;
+    std::unique_ptr<MP3File> musicFile;
+    std::atomic<bool> haveMusicFile;
+    std::unique_ptr<std::thread> musicFeed;
+    std::atomic<bool> exitMusicFeedThread;
+    int android_fd;
+    void initRubberBand();
+    void closeRubberBand();
+    void closeMusicFile();
+    void musicFeedThread();
 };
 
 #endif //LOCKSTEP_PLAYBACKENGINE_H