MPA Decoder is enabling you to decode MPA files. MPA is an MPEG-2 audio file which does not contain video and which is usually recommended for web users.
The format is supported by a variety of media players.
In order to install MPA Decoder, you need to use the same installation method that is recommended with DLL and AX codec files. See How to install/uninstall DLL and AX codec files
The latest versions of MPA Decoder have been added several improvements: added support for decoding MEDIASUBTYPE_SIPR_WAVE - SIPR in .wmv, Voxware MetaSound; changed test for Bitstream/SPDIF output support; repaired conversion to AC3 and corrected work with DTS-HD streams for output to S / PDIF output.
The size of the audio file is reduced and sounds can be downloaded more easily.