there's a very shocking pronouncing mistake here! 'Jean' is a proper noun and pronounced /ʒɑ̃~/ as it is in the recording, but 'jean' (the trousers) are never pronounced like that and french people would actually have trouble understanding what this referred to if used so. The recording should say /dʒi:n/.
Very precisely. Unless of course you mean that your friend Jean (Dujardin) is long... This word was taken from english and is pronounced like in english, except that it can be singular to designate a single pair of trousers (and still keep its "s", "un jeans" as opposed to "la toile de jean", the fabric, although I believe "un jean" is accepted). In plural form however, although written as in english "jeans", the ending s is generally not pronounced. If it is, it is part of the way the person likes to pronounce this foreign word, and not a specific mark of plural. As a matter of fact, "jeans" is not an easy word, and I think it would be better to learn "pantalon".
There are a few words in French that are treated differently than the comparable word in English. Specifically, (a pair of) trousers = un pantalon. The word "trousers" in English can refer to a single item of clothing or multiple items. That is why English speakers sometimes use the phrase "a pair of" when referring to the singular. If you say "a pair of trousers", it is clearly singular and you would use the singular "is" in English. If you say "trousers" (whether you mean singular or plural), you will say "are" in English. That's just the way it is. The same applies to "un jean" = (a pair of) jeans.