This parish from where this video came is the home of our esteemed colleague, Mr. Jeffrey Morse. I would think he'd be more than happy to answer your questions. Contact information may be found here: http://www.sacfssp.com/
The first piece on the video sounds like Sir David Willcock's arrangement of "The Angel Gabriel From Heaven Came." You can find it in Carols for Choirs volumes 2 and 3 and in 100 Carols for Choirs (#94), published by Oxford University Press. In these collections it has the title "Gabriel's Message."
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