This is the Elysium Quartet performing Karlheinz Stockhausen's Helicopter String Quartet as part of the world premiere of the opera Mittwoch aus Licht by the Birmingham Opera Company 22.08.12. It was written between 1995 and 1997. There are other days in the week, but he didn't finish the whole cycle.
It didn't get its premiere until this year, so if you missed it, you may not get a second chance. Feel free to skip around in the video.