查找MPEG2

查找原生 MPEG2 包含和库

这个模块定义

MPEG2_INCLUDE_DIR, path to mpeg2dec/mpeg2.h, etc.
MPEG2_LIBRARIES, the libraries required to use MPEG2.
MPEG2_FOUND, If false, do not try to use MPEG2.

也有定义，但不是一般用途

MPEG2_mpeg2_LIBRARY, where to find the MPEG2 library.
MPEG2_vo_LIBRARY, where to find the vo library.