The problem is that the MORE you crop, the MORE resolution is lost. "Deep" cropping (don't know the correct term) will cause problems.
For example - you start with a 1920x1080 clip, then crop it down to (say) 960x540... then you produce that and re-use the cropped version in the main production... which you produce to 1920x1080. That cropped clip can't get pixels from nowhere. They'll get stretched to fill the screen... do you see what I mean?
I guess the best thing is to crop in moderation!
Whatever you do with pre-production, stick to the same format & profile as your original clips.
Cheers - Tony
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