Android：如何从LibVLC获取字幕列表？

Question

我在lib下使用了

compile 'de.mrmaffen:libvlc-android:2.1.12@aar'

这就是我创建媒体播放器的方式

// Create LibVLC
        // TODO: make this more robust, and sync with audio demo
        ArrayList<String> options = new ArrayList<String>();
        //options.add("--subsdec-encoding <encoding>");
        options.add("--aout=opensles");
        options.add("--audio-time-stretch"); // time stretching
        options.add("-vvv"); // verbosity
        libvlc = new LibVLC(this, options);

        // Creating media player
        mMediaPlayer = new MediaPlayer(libvlc);
        mMediaPlayer.setEventListener(mPlayerListener);


        // Seting up video output
        final IVLCVout vout = mMediaPlayer.getVLCVout();
        vout.setVideoView(mVideoView);
        //vout.setSubtitlesView(mSurfaceSubtitles);
        vout.setWindowSize(mWidth, mHeight);
        vout.addCallback(this);
        vout.attachViews();
        //            vout.setSubtitlesView(tv_subtitle);


        Media m = new Media(libvlc, Uri.parse(media));
        mMediaPlayer.setMedia(m);
        mMediaPlayer.play();

我尝试获得如下字幕：

// MediaPlayer.getSpuTracks() - Get the list of available spu (subtitle) tracks.
MediaPlayer.TrackDescription[] trackDescriptions = mMediaPlayer.getSpuTracks();
for (int i = 1; i < trackDescriptions.length; i++) {
    MediaPlayer.TrackDescription description = trackDescriptions[i];
    Log.i(TAG, "loadSpuTrack " + description.name + ", id " + description.id);
}

但它为我提供了null，我确定我有字幕。还有其他的电影来获得字幕吗？