I'm not sure how the download links work on that website, so unfortunately I can't help with the issue. The player expects a direct download link to an mp4 or webm video. It works better if the link has a html download attribute, but it should also work if the link ends in ".mp4" or ".webm". If you see the title load but the video doesn't play, then something else is preventing the player from streaming the video (could be a security key assigned to the download link doesn't work when ExoPlayer streams the video).