Need codec to play mp4 in WMP 11

When I download a youtube musical mp4, my Windows Media Player tells
me it cannot play the file because I do not have the proper codec.  I
did set mp4 in the File Types menu to no avail.

I know that some of these freebie codecs have tons of ad crap and
assorted garbage toolbars that come with them.  Is there a trustworthy
freebie that I can download?  I am using Win XP and WMP 11.

I should add that I do not want a separate player such as VLC.

I should add that I do not want a separate player such as VLC.  I want
to be able to play the mp4s in WMP 11.

Installing Haali's Media Splitter (also known as MatroskaSplitter)

Installing Haali's Media Splitter (also known as MatroskaSplitter) -
http://haali.su/mkv - and FFDShow -
http://www.free-codecs.com/download/FFDshow.htm - will allow WMP to play
MP4 files.

Regards

--
Tim De Baets
http://www.bm-productions.tk