private void adjustAspectRatio(int videoWidth, int videoHeight) {
        int viewWidth = textureView.getWidth();
        int viewHeight = textureView.getHeight();
        double aspectRatio = (double) videoHeight / videoWidth;

        int newWidth, newHeight;
        if (viewHeight > (int) (viewWidth * aspectRatio)) {
            // limited by narrow width; restrict height
            newWidth = viewWidth;
            newHeight = (int) (viewWidth * aspectRatio);
        } else {
            // limited by short height; restrict width
            newWidth = (int) (viewHeight / aspectRatio);
            newHeight = viewHeight;
        }
        int xoff = (viewWidth - newWidth) / 2;
        int yoff = (viewHeight - newHeight) / 2;
        /*Log.v(TAG, "video=" + videoWidth + "x" + videoHeight +
                " view=" + viewWidth + "x" + viewHeight +
                " newView=" + newWidth + "x" + newHeight +
                " off=" + xoff + "," + yoff);*/

        Matrix txform = new Matrix();
        textureView.getTransform(txform);
        txform.setScale((float) newWidth / viewWidth, (float) newHeight / viewHeight);
        //txform.postRotate(10);          // just for fun
        txform.postTranslate(xoff, yoff);
        textureView.setTransform(txform);
    }



private void checkMultiAudioTrack(MediaPlayer mediaPlayer) {
        mediaPlayer.pause();
        MediaPlayer.TrackInfo[] trackInfo = mediaPlayer.getTrackInfo();

        ArrayList<Integer> audioTracksIndex = new ArrayList<>();

        for (int i = 0; i < trackInfo.length; i++) {
            if (trackInfo[i].getTrackType() == MediaPlayer.TrackInfo.MEDIA_TRACK_TYPE_TIMEDTEXT) {
                audioTracksIndex.add(i);
            }
        }

        AlertDialog.Builder builder = new AlertDialog.Builder(VideoPlayer.this);
        builder.setTitle("Select Subtitle Track");
        String[] values = new String[audioTracksIndex.size()];
        for (int i = 0; i < audioTracksIndex.size(); i++) {
            values[i] = i + "." + trackInfo[i].getLanguage().replace("und", "Unknown");
        }
        /*
         * SingleChoice means RadioGroup
         * */
        builder.setSingleChoiceItems(values, 0, (dialog, which) -> mediaPlayer.selectTrack(which))
                .setPositiveButton("Ok", (dialog, which) -> {
                    mediaPlayer.selectTrack(which);
                    mediaPlayer.start();
                    dialog.dismiss();
                }).setNegativeButton("Cancel", (dialog, which) -> dialog.dismiss());
        builder.show();
    }