title: MediaRetriever for artist returning null
body: <p>artist is gettiing initialised value only,.not the artistextracted using metadata
  plz suggest me wat wrong i am  doing </p>
  
  <pre><code> Strng artist="";
          void onCreate(){
              metaRetriver1 = new MediaMetadataRetriever();
              metaRetriver1.setDataSource("/storage/sdcard0/Tu+Jo+Hain.mp3");
  
              artist=metaRetriver1.extractMetadata(MediaMetadataRetriever.METADATA_KEY_ARTIST);
  
          }
  </code></pre>