What codec are you capturing in? If your capturing into mp2 or mp4 which seems to be the situation for some of these home Hd cams that record to hard drives, I wouldn’t just because the mp files are already compressed. However if your capturing to p2 cards or tape, then I would definitely change the resolution. It also depends on your delivery. Are you going to an h264 flash video for the web? If so then if your recording with the mp4 codec, I wouldn’t change the settings. However, if your recording to something like flash 6 I don’t think the mp4 codec will make much of an impact when you compress it. Again, it all depends on how your capturing imho.
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