fix: play with rate of mp3 file

TODO.md

@@ -3,6 +3,7 @@
 * analyze the (secondly or so) noise beeps in the mp3 playback
   - introduced with this commit
   - is it librubberband, my failure to feed it properly (buffer exhaustion), or sth else?
+  - the sizes of my buffers?
 
 * correct sampling rate of libmpg123 vs. 48000 Hz using librubberband
 

app/src/main/cpp/PlaybackEngine.cpp

@@ -80,7 +80,9 @@ PlaybackEngine::PlaybackEngine(std::string filesDir, int resid):
     mFilesDir(filesDir),
     haveMusicFile(false),
     exitMusicFeedThread(false),
-    android_fd(0)
+    android_fd(0),
+    haveTimeRatio(false),
+    timeRatio(1.0)
 {
     LOGI("PlaybackEngine()");
     LOGI("NDK LOG_LEVEL=%d", LOG_LEVEL);
@@ -162,6 +164,12 @@ void PlaybackEngine::musicFeedThread() {
 
     // thread 2: polling for decoding more mp3 -> process()  -- getSamplesRequired()
     while(!exitMusicFeedThread.load()) {
+
+        if(haveTimeRatio.load()) {
+            stretcher.setTimeRatio(timeRatio);
+            haveTimeRatio.store(false);
+        }
+
         // do work ...
         size_t num_samples = stretcher.getSamplesRequired();
 
@@ -260,6 +268,10 @@ void PlaybackEngine::playMusic(int fd) {
 
     android_fd = fd;
     musicFile.reset(mp3file_open_fd(android_fd, 0));
+    if(musicFile) {
+        timeRatio = ((double) 48000) / ((double) musicFile->rate);
+        haveTimeRatio.store(true);
+    }
     haveMusicFile.store(true);
     mPlayer->setMusic(std::make_shared<MusicProvider>(&stretcher));
 }

app/src/main/cpp/PlaybackEngine.h

@@ -46,6 +46,8 @@ private:
     std::unique_ptr<std::thread> musicFeed;
     std::atomic<bool> exitMusicFeedThread;
     int android_fd;
+    std::atomic<bool> haveTimeRatio;
+    double timeRatio;
     void initRubberBand();
     void closeRubberBand();
     void closeMusicFile();