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.
IRCAM SDIF (Institut de Recherche et Coordination Acoustique/Musique Sound Description Interchange Format). Used by academic music software such as the CSound package, and the MixView sound sample editor.