Time for action – playing background music

Let's open and play an MP3 music file with OpenSL ES:

1. MP3 files are opened by OpenSL using a POSIX file descriptor pointing to the chosen file. Improve jni/ResourceManager.cpp created in the previous chapters by defining a new structure ResourceDescriptor and appending a new method descriptor():

   ...
   struct ResourceDescriptor {
       int32_t mDescriptor;
       off_t mStart;
       off_t mLength;
   };
   
   class Resource {
   public:
       ...
       status open();
       void close();
       status read(void* pBuffer, size_t pCount);
   
       ResourceDescriptor descriptor();
   
       bool operator==(const Resource& pOther);
   
   private:
       ...
   };
   #endif

2. Implement jni/ResourceManager.cpp. Of course, makes use of the asset manager API to open the descriptor and fill a ResourceDescriptor structure:

   ...
   ResourceDescriptor Resource::descriptor() {
       ResourceDescriptor lDescriptor = { -1, 0, 0 };
       AAsset* lAsset = AAssetManager_open(mAssetManager, mPath,
                               ...