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90 Everything You Ever Wanted to Know About DVD<br />
1.2 millimeters thick, made of two 0.6-millimeter substrates glued together.<br />
These are the same form factors as a CD. A DVD can be single-sided or<br />
double-sided. Each side can have one or two layers of data. The amount of<br />
video a disc can hold depends on how much audio accompanies it and<br />
how heavily the video and audio are compressed. The oft-quoted figure of<br />
133 minutes is apocryphal; a DVD with only one audio track easily holds<br />
over 160 minutes, and a single layer can actually hold up to 9 hours of video<br />
and audio if it’s compressed to VHS quality.<br />
At a rough average rate of 5 Mbps (4 Mbps for video and 1 Mbps for 2<br />
or 3 tracks or audio), a single-layer DVD can hold a little over 2 hours. A<br />
dual-layer disc can hold a 2-hour movie at an average of 9.5 Mbps (close<br />
to the 10.08 Mbps limit).<br />
A DVD-Video disc containing mostly audio can play for 13 hours (24<br />
hours with dual layers) using 48/16 PCM (slightly better than CD quality). It<br />
can play 160 hours of audio (or a whopping 295 hours with dual layers)<br />
using Dolby Digital 64 kbps compression of monophonic audio, which is<br />
perfect for audio books.<br />
DVD Capacities<br />
For reference, a CD-ROM holds about 650 MB, which is 0.64 gigabytes or<br />
0.68 billion bytes. Table 3-1 outlines the capacities of all the different versions<br />
of DVDs. SS/DS means single-sided/double-sided, SL/DL/ML means<br />
single-layer/dual-layer/mixed-layer (mixed means single layer on one side<br />
and dual layer on the other side), gig means gigabytes (2 30 ) and BB means<br />
billions of bytes (10 9 ). See note about giga versus billion in “Notation and<br />
Units” in <strong>Chapter</strong> 7, “Leftovers.”<br />
TABLE 3-1 Various DVD Capacities<br />
DVD-5 (12 cm, SS/SL) 4.37 gig (4.70 BB) of data, over 2<br />
hours of video<br />
DVD-9 (12 cm, SS/DL) 7.95 gig (8.54 BB), about 4 hours<br />
DVD-10 (12 cm, DS/SL) 8.74 gig (9.40 BB), about 4.5 hours<br />
DVD-14 (12 cm, DS/ML) 12.32 gig (13.24 BB), about 6.5 hours<br />
DVD-18 (12 cm, DS/DL) 15.90 gig (17.08 BB), over 8 hours<br />
DVD-1 (8 cm, SS/SL) 1.36 gig (1.46 BB), about half an hour<br />
DVD-2 (8 cm, SS/DL) 2.47 gig (2.66 BB), about 1.3 hours<br />
DVD-3 (8 cm, DS/SL) 2.72 gig (2.92 BB), about 1.4 hours<br />
DVD-4 (8 cm, DS/DL) 4.95 gig (5.32 BB), about 2.5 hours
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