[ excerpt from developer's site ]
It is a free library for decoding mpeg-2 and mpeg-1 video
streams. The main goals in libmpeg2 development are:

Conformance - libmpeg2 is able to decode all mpeg streams that
conform to certain restrictions: "constrained parameters" for
mpeg-1, and "main profile" for mpeg-2. In practice, this is what
most people are using. For streams that follow these restrictions,
we believe libmpeg2 is 100% conformant to the mpeg standards - and
we have a pretty extensive test suite to check this.

Speed - for most current systems, the display will actually take
more time than the mpeg-2 decoding. For systems that have hardware
color conversion and scaling (as we can use with the xv extension
in Xfree 4), you should be able to watch DVD streams on a Celeron
400. On a PIII/666 with null display you should get about 110 frames
per second.

Portability - most of the code is written in C, and when we use
platform-specific optimizations we always have a generic C routine
to fall back on.