The Mass is being offered in celebration of the anniversary of the pontificate of Pope Benedict XVI.
Here are some stills from that to give you a sense of the occasion.
The vesting prayers
One can see the basilica is filled to capacity
The prayers at the foot of the altar
The incensation of the altar
The subdeacon chants the epistle
A very nice view of the original high altar of the basilica. The altar is covered by a wonderful ciborium.
The NLM hopes to provide you more photos from the official photographs that were no doubt taken for the Mass.