So let's be clear, the above video is NOT what Offertory is about as much as it might seem that way. The Liturgy of the Word is over, we take a seat, music plays, it seems as though a bunch of technical stuff is taking place such as the taking up of the collection, the preparation of the altar, the gifts are brought forward, music takes place, and at the end the first thing we do is stand and seem to pick up with part II.
But notice what doesn't happen. We don't make the announcements. If this were just a "killing time" moment, this would be the PERFECT time to make announcements: those who were late are there by now and it is before the time of those who sneak out after receiving Communion. But this is just as much a part of the liturgical action as any other part of the Mass. This is not just a convenient time to take up the collection. Even the collection itself is a liturgical action: the members of the Church offering some of their gifts back to God and the community to carry on the work of Christ. That is why I usually tell people even if they can't give of if they give electronically, they should drop an empty envelope in the collection and offer a prayer for the parish.
The bread and wine which will become the Body and Blood of Christ is brought forward - preferably by some in the congregation. Other gifts may be brought forward (such as the collection, gifts for the poor, and such but these are placed in an appropriate place AWAY from the altar.