After transferring video from a miniDV tape to my Powerbook I noticed that about 60 minutes of video takes roughly 11GB (or nearly 3 DVD's!). Now, a purchased DVD movie will have 2 to 2.5 hours of video plus bonus materials often on only one disc. Could someone help me understand this? Do I need to compress my video somehow before burning it to DVD? Thanks.
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Question - iMovie file sizes
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Re: Question - iMovie file sizes
Just to elaborate on a couple of points...
As 7on already pointed out, iDVD 4 can put up to 2 hours of video on a DVD-R. This is because, yes, the video gets compressed. The nice part is that iDVD does it for you automatically. The video compression scheme used on DVD is MPEG2. It's actually quite good at compression of video file sizes, so the tradeoff is that it takes a rather long time to do - on my 733 G4 it takes at least 2-3 times realtime to compress the video for a DVD. I'm sure a shiny dual G5 does a little better, though!
appleretailguy noted that commercial DVDs use a different format than DVD-Rs. Basically, a DVD-R has a single data layer which holds about 4.2 GB. You can see that obviously in order to cram 2 hours of video (about 26 GB uncompressed) onto a single disc, iDVD has to work pretty hard to compress it to MPEG2 and still keep it looking good! Commercial discs are usually dual layer - basically they have double the capacity because there's one data layer sandwiched on top of another. The laser for a DVD reader can somehow differentiate between layers (not sure of the exact details, but it has one mode where it can see the surface layer, and another mode where it sees through the surface layer to the inner layer). But I guess they couldn't figure out how to make DVD writers burn two different layers this way, so we only get half the capacity in discs we create ourselves.
More than you wanted to know, probably!
Just to elaborate on a couple of points...
As 7on already pointed out, iDVD 4 can put up to 2 hours of video on a DVD-R. This is because, yes, the video gets compressed. The nice part is that iDVD does it for you automatically. The video compression scheme used on DVD is MPEG2. It's actually quite good at compression of video file sizes, so the tradeoff is that it takes a rather long time to do - on my 733 G4 it takes at least 2-3 times realtime to compress the video for a DVD. I'm sure a shiny dual G5 does a little better, though!
appleretailguy noted that commercial DVDs use a different format than DVD-Rs. Basically, a DVD-R has a single data layer which holds about 4.2 GB. You can see that obviously in order to cram 2 hours of video (about 26 GB uncompressed) onto a single disc, iDVD has to work pretty hard to compress it to MPEG2 and still keep it looking good! Commercial discs are usually dual layer - basically they have double the capacity because there's one data layer sandwiched on top of another. The laser for a DVD reader can somehow differentiate between layers (not sure of the exact details, but it has one mode where it can see the surface layer, and another mode where it sees through the surface layer to the inner layer). But I guess they couldn't figure out how to make DVD writers burn two different layers this way, so we only get half the capacity in discs we create ourselves.
More than you wanted to know, probably!