How to make full-screen video viewing using Exoplayer without stretching it

Question

I use ExoPlayer to show the video, currently I just maintain the default aspect ratio, but this is not ideal as I want the video to fully display.

        for (Listener listener : mListeners) {
        listener.onVideoSizeChanged(width, height, pixelWidthHeightRatio);
    }

I tried to adjust the video to the full width of the screen, however it just stretches and distorts the video. Any idea how to scale the video up while maintaining the height to width ratio?