Ok I'll try and link one in my dropbox. Yeah the file size is big but they are definitely music files, not video files. They are primarily used for DJ controllers to be able to isolate the bass, vocals, drums etc for mixing while still containing a master track to be played by any normal music player. It's fairly new music format created by Native Instruments.
https://www.dropbox.com/s/syz6wlqygt451s4/253_Opa_Locka.stem.mp4?dl=0