private void initializePlayer() {

        trackSelector = new DefaultTrackSelector();

        MappingTrackSelector.MappedTrackInfo trackInfo = trackSelector.getCurrentMappedTrackInfo();

        if (trackInfo == null)

            return;



        DefaultTrackSelector.Parameters parameters = trackSelector.getParameters().buildUpon()

                .setSelectionOverride(1, trackInfo.getTrackGroups(1),

                        new DefaultTrackSelector.SelectionOverride(1, 1))

                .build();

        trackSelector.setParameters(parameters);



        player = ExoPlayerFactory.newSimpleInstance(this, trackSelector);

        playerView.setPlayer(player);

        player.setPlayWhenReady(true);

        player.seekTo(currentWindow, playbackPosition);

        DataSource.Factory dataSourceFactory = new DefaultDataSourceFactory(this,

                Util.getUserAgent(this, "ExoPlayer"));

        Uri uri = Uri.parse(Environment.getExternalStorageDirectory() + "/Movies/3dall.mp4");

        MediaSource videoSource = new ExtractorMediaSource.Factory(dataSourceFactory)

                .createMediaSource(uri);

        player.prepare(videoSource);

    }

第一次用ExoPlayer
实现视频的语言切换，trackInfo 一直是null
new DefaultTrackSelector.SelectionOverride(int groupIndex, int... tracks)中的参数一直没搞明白是什么
第一个是语言索引？第二个是什么