The choir member in the front row on the left (from the viewer's perspective) changes between close up shots and shots from the crowd.
The movie takes place just before Christmas, and it was shot in the winter. However, there is a small difference between mid December and late February / early March - you can hear loud singing by singing birds in the few outdoor scenes (the vast majority of the movie takes place indoor), and they don't sing between early autumn and late February / early March.