What are Microsoft codecs?

[gilpel at altern.org]

What are Microsoft codecs? Is it more than an encapulation of MP4? What's
the legal status of MP4? Once you have at hand the
compression/decompression algorithms -- which must have been developed by
mathematicians decades ago -- is there so much work involved in writing
codecs? Has the reason they weren't developed before more to do than with
the fact the CPUs weren't powerful enough to use them?

In other words, are codecs more than a marketing scheme, just as were the
"codecs" for Word  and Excel documents? 'Cause, if you save a Word file to
odt format, the size will shrink by about 75%. (I must admit I checked
this with rtf vs odt, but I suppose it's at least as bad with doc format.)
It seems the extra code's only purpose is to make decryption more
difficult.

Isn't this the same with MWV codecs?