i.e. “unique material filmed over the course of the last three years”
I think this is stylistically neat here.

E.g.:
Helena Trestíková is famous for her “časosběrné natáčení” (“téma se rodí v case”1). Her “René” is described as “An intimate portrait of a man on the edge of society, filmed over the course of twenty years.”2

1. http://webcache.googleusercontent.com/search?q=cache:ghEGQpA...
2. http://www.imdb.com/title/tt1334606/


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Note added at 1 day30 mins (2013-12-30 14:05:54 GMT)
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(In your second sentence, "časosběrný materiál", as proposed by babylondon, would be "footage".)