IDVD File Sizes

Ok, so I'm very confused now.

I'm running IDvd on my Macbook Pro.

I have a collection of .avi files which I want to put onto a disk with a simple title menu. There are 13 files in all, which total 3.65gb.

When trying to use IDvd I can't get more than 4 of these files on to a disk without it telling me that I have exceeded the maximum content duration. The files are about 20 minutes long, so that's less than a normal movie.

Also, the size of the files are over 4.4gb! How can 4 files + menu, total more than the original 13 files?

Because you're comparing apples to oranges for storage codecs in terms of space.

Your AVI's are probably very highly compressed files with say a DivX or XviD codec. DVD's playable on a DVD player (not including DVD players that can play video files stored on a DVD) require the DVD to have video in a MPEG or MPEG2 stream. MPEG2 streams take a lot more space then those highly compressed AVIs. The only way to fit more on a DVD is to reduce the average bit rate (or constant bit rate depending on whether the encoder is using CBR or VBR). You can reduce the quality of the iDVD output and possibly fit more on the disc, but iDVD is limited to how much control you have over the final size. MPeg2 will explode in size quickly the longer the video output is. For example, let's say you have a video that's 1 hr long and takes 300-400mb in an avi. You take it to a DVD encoder that will do an VBR of 4000kbps (which means your average bit rate will be 4mbps, some points in the movie will be higher bit rate, some will be lower but we'll stick with the 4mbps for calculations, I think iDVD sets a higher bit rate), that 1 hr video, 60 minutes, 3600 seconds - that's ~14,400 mbits - now divide that by 8 and you get: 1,800 mbytes. You've just seen the file go from 300-400 mbytes to 1.8 gbytes. And that's a medium quality, and it doesn't take in account bit rate spikes or luls which may push that one file to 2+gigs. Many use 6mbps avg.

Usually on a single layer DVD I put between 1 and 2 hrs of video depending on how much quality loss is acceptable.

I know there is a setting in iDVD to reduce the quality/increase compression. I've seen it before, but honestly, I never remember where it is.