Eighteen data DVDs? That's nuts. Should have used a portable drive. And if you had compressed to video DVDs, that would be even worse -- you lost three generations' worth of image quality. You did this to save something like $20 of postage? The drive itself would cost more, but you can reuse it.
Another approach to try next time is to see if they'll allow you to compress the internet downloads yourself, sending them one clip first as a proof to see if they're satisfied. Not all clients will accept that, but if they do, you could have delivered the files over the internet.
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