if you cant capture in fcp i do not know what to tell you.
however, you do not need to blow the clips up 130%. that in its self started your problem.
convert the footage to what you need with compressor then edit. i used imovie for my very first video job. it is a good app but not pro grade. it sounds like you imported the footage wrong thus the need to blow them up.
artifacts are square or puzzle shaped portions of your video that seem melted or extremely blurred. a good example of what an artifact would be the mosaic tiles they use to obscure someones face. not the blur but the small array of squares they use for anonymity.
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What you do with what you have, is more important than what you could do, with what you don't have."
> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"