you can try to use a youtube downloader to download videos to your Mp3, here is the one i use for long which can not only download videos from youtube but also convert videos to Mp3 while it is downloading. hope this helps for you.
Windows Media player has limited options for playing different formats of file. But it can be corrected. Try download the full CODEC pack. You can get it free, but always choose the advanced options from the download site, as it might try and change or add new browsers or other software.
Once installed it should play any file.