A medieval mystery

What is this early chant all about?

The assiduous reader will have seen this one in these pages some years ago. It’s worth another run. (I won’t ask if you can sing it)

Here’s the full text in case you can’t read it:

Reno erat Rudolphus / Nasum rubrum habebat;
Si quando hunc videbas, Hunc candere tu dicas.

Omnes tarandri alii / Semper hunc deridebant;
Cum misero Rudolpho / In ludis non ludebant.

V. Sanctus Nicholas dixit / Nocte nebulae,
“Rudolphe, naso claro / Nonne carum tu duces?”

Tum renores clamabant, / “Rudolphe, delectus es?
Cum naso rubro claro / Historia descendes!”

You can listen to the music here>.  As experienced chanters by now, you will also be able to tell me what style of music this is.

Hint: it’s about a traditional Christmas theme, if you hadn’t guessed. Send your answer: