The *.m2v files are normally destined to be multiplexed (muxed), which is the process of adding audio data and perhaps other streams such as subtitles, before use. M2Vs are created by demultiplexing (demuxing) an existing MPEG-2, or by converting another video format to MPEG-2. The file extension m2v is mostly found with SFV Host Files.
WavPack lossless audio compression. Note that, when converting .wav to this format and back again, the RIFF header is not necessarily preserved losslessly (though the audio is).