This is sacred music from pre-Reformation England. Sarum is old name for the town of Salisbury and it disappeared as a form of the Church's liturgy after the Council of Trent. However, it was retained in some form as it became the basis of Anglican church music and for the Book of Common Prayer.  The concert takes place in a New York Episcopalian church - Trinity Church. I heard about it because it was posted onto my Facebook page by a TMC student who is currently out in Rome - thanks Taylor! Access the video through the image of Salisbury Cathedral below.