If you just want to develop a personalized player and you want to finish it as soon as possible you could simple use Visual Basic and exploit the power of the media libraries of windows.

C++ is also a good language to start with, but the route is too steep. There are lots of libraries and codecs usage examples on this language.

If you want to develop a lightweight and cross platform media player. your best bet is to you use Java with Java Media Framework.

I hope that I become of any help with you.

Thanks!