The video doesn't really go into much depth about the Assumption, and it still manages to mess a few things up.
1) It poses the question: "Do you know what year the feast of the Assumption of the Blessed Virgin Mary was declared official Catholic teaching?"
What he's going for obviously is the 1950 definition of the dogma of the Assumption. What was defined was specifically a dogma, not the feast as such.
The feast of the assumption has been around a much longer time, in various places - and at various times, not just August 15. The feast came in during the early part of the middle ages, although celebrated in various ways. For example, the "Catholic Encyclopedia documents the following, under the entry for the feast of the assumption:
Some of the Bavarian dioceses and those of Brandenburg, Mainz, Frankfort, etc., on 23 Sept. kept the feast of the "Second Assumption", or the "Fortieth Day of the Assumption" (double) believing, according to the revelations of St. Elizabeth of Schönau (d. 1165) and of St. Bertrand, O.C. (d. 1170), that the B.V. Mary was taken up to heaven on the fortieth day after her death (Grotefend, Calendaria 2, 136). The Brigittines kept the feast of the "Glorification of Mary" (double) 30 Aug., since St. Brigitta of Sweden says (Revel., VI, l) that Mary was taken into heaven fifteen days after her departure (Colvenerius, Cal. Mar., 30 Aug.). In Central America a special feast of the Coronation of Mary in heaven (double major) is celebrated 18 August. The city of Gerace in Calabria keeps three successive days with the rite of a double first class, commemorating: 15th of August, the death of Mary; 16th of August, her Coronation.
2) Additionally, the clip asserts that there have been only two exercises of papal infallibility - this definition, and the definition of the Immaculate Conception. He goes so far as to say, "In the two thousand year history of the Catholic Church, infallibility has only been exercised twice."
I think that practically all Roman Catholic scholars would agree that those two are times when the pope attempted to speak infallibly, but there is a very open question about whether there have been other examples throughout history where a pope has used this alleged gift of infallibility.
The council, Vatican I, that defined the dogma of papal infallibility did not seem to suggest that it was granting the pope a new power that he had never had before. Consequently, one would assume that the pope would have exercised it at some point in the preceding centuries.
The moral of the story is this - a lot of Roman Catholics don't know a lot about their religion. Even the priest running the program claims he had to look up when the Assumption was defined. If you are going to evangelize Roman Catholics, you need to know their religion better than they do, rather than relying on them to explain to you what their religion teaches.
By the same token, the priest's final question and its answers should be taken to heart. His question is "what does the assumption mean for you?" This subjective approach is something that none of the folks he asks have any problem answering. They may not know when the feast is celebrated, or what pope defined the dogma (Pius XII), but they can apply it subjectively to themselves. And these subjective responses can actually help to reveal the flaws in the religion.
For example, in this case, what it means to several of the people is - in essence - hope in the resurrection. But the Holy Scriptures teach us that our hope in the resurrection is not grounded in the assumption of Mary, but in the resurrection of Jesus Christ:
Acts 17:31 Because he hath appointed a day, in the which he will judge the world in righteousness by that man whom he hath ordained; whereof he hath given assurance unto all men, in that he hath raised him from the dead.
Another response was that it gives assurance that Mary is in heaven working and praying "for me and everyone." But again, this is Mary usurping the role Biblically given to Jesus:
And they truly were many priests, because they were not suffered to continue by reason of death: but this man, because he continueth ever, hath an unchangeable priesthood. Wherefore he is able also to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them.
So, when you are talking to your Roman Catholic friends and relatives, be sure to ask the important question about what their religious observances mean to them. Sometimes those answers can be more revealing both to them and to you, than an encyclopedic knowledge of Ott's Fundamental of Catholic Dogma. While it is important to be familiar with their religion, it is even more important to get to know them personally.
There will be some who will not know the difference between the feast of the ascension and the feast of the assumption, and there will be some who not only know the difference but observe them both as holy days. More importantly, don't be the one to tell a Roman Catholic that their doctrine of the Assumption puts Mary in the place of Jesus. Let them explain it to you, and then explain to them why their religion - even those parts only defined last century - is in conflict with Holy Scripture.
(Thanks to Francis Beckwith for bringing this clip to my attention.)