¿Por qué mi SeekBar no se actualiza?

Implementé una barra de búsqueda en mi aplicación que es un simple reproductor de música. Pero cuando reproduzco la música (recibida de uri) simplemente no se actualiza al ejecutarse. Pero cuando lo muevo a alguna posición, mueve la canción allí. ¿Alguna idea de cómo resolver este problema?

Mi código:

public class MusicPlayer extends ThemableActivity implements SeekBar.OnSeekBarChangeListener {
MediaPlayer musicPlayer;

@Override
protected void onCreate(Bundle SavedInstanceState) {
    super.onCreate(SavedInstanceState);
    setContentView(R.layout.media_player_layout);
    Intent intent = getIntent();
    String track = intent.getDataString();
    TextView txt = (TextView)findViewById(R.id.txt);
    txt.setGravity(Gravity.CENTER);
    txt.setText(track);
    ImageView img = (ImageView)findViewById(R.id.img);
    img.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
    final Uri uri = getIntent() != null ? getIntent().getData() : null;
    final SharedPreferences premiumSettings = getSharedPreferences("PREMIUM", Context.MODE_PRIVATE);
    final boolean isPremium = premiumSettings.getBoolean("isPremium", false);
    final SeekBar seekBar = (SeekBar) findViewById(R.id.seekBar);
    seekBar.setOnSeekBarChangeListener(this);


    if (isPremium) {
        musicPlayer = MediaPlayer.create(MusicPlayer.this, uri);
        seekBar.setMax(musicPlayer.getDuration()/1000);
        musicPlayer.start();
        final ImageButton play = (ImageButton) findViewById(R.id.play);
        if(!musicPlayer.isPlaying()){

            play.setImageResource(android.R.drawable.ic_media_play);
        }
        else{
            play.setImageResource(android.R.drawable.ic_media_pause);

        }
        play.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int position = musicPlayer.getCurrentPosition();
                if(musicPlayer.isPlaying()){
                    musicPlayer.pause();
                    play.setImageResource(android.R.drawable.ic_media_play);

                }
                else {
                    musicPlayer.seekTo(position);
                    musicPlayer.start();
                    play.setImageResource(android.R.drawable.ic_media_pause);

            }}
        });
        final Handler mHandler = new Handler();
        Runnable mRunnable = new Runnable() {

            @Override
            public void run() {
                if(musicPlayer!=null){
                    int mCurrentPosition = musicPlayer.getCurrentPosition() / 1000;
                    seekBar.setProgress(mCurrentPosition);
                }
                mHandler.postDelayed(this, 1000);
            }
        };

        ImageButton exit = (ImageButton) findViewById(R.id.exit);
        exit.setImageResource(android.R.drawable.btn_dialog);
        exit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (musicPlayer.isPlaying()) {
                    musicPlayer.stop();
                }
                    musicPlayer.release();
                    musicPlayer = null;
                    finish();

            }
        });


    }
    else {
        AlertDialog.Builder builder = new AlertDialog.Builder(MusicPlayer.this);
        builder.setTitle("Error");
        builder.setMessage("You are not premium user. Please enter the promocode or buy the full version");
        builder.setIcon(R.drawable.holo_dark_action_info);
        builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int whichButton) {
                finish();
            }
        });
        AlertDialog dialog = builder.create();
        dialog.show();
    }}
public void onBackPressed () {
        if(musicPlayer.isPlaying()) {
            musicPlayer.stop();
        }
            musicPlayer = null;
        finish();
}

@Override
public void onProgressChanged(SeekBar seekBar, int i, boolean b) {
    if (musicPlayer != null && b){
        musicPlayer.seekTo(i * 1000);
    }

}

@Override
public void onStartTrackingTouch(SeekBar seekBar) {

}

@Override
public void onStopTrackingTouch(SeekBar seekBar) {

}