Posted by Abdul Rassa at crtntx1-ar2-171-235.dsl.gtei.net on March 27, 2001 at 00:57:38:
In Reply to: DVD Q for Vincent (or anyone who can answer) posted by Golgothan on March 26, 2001 at 21:41:23:
Audio and Video for dvd's is compressed using the MPEG-2 codec. I have plenty of DVD's ripped onto CD's using the MPEG-4 codec. Using the MPEG-4 codec you can compress about 1 hour of audio and video down to about 350 megs of data.
(I copied the following from an information website)
The DVD-ROM, DVD-Video and DVD-Audio Formats have storage capacities between 4.7 to 17.0 GBytes. The variation in total storage capacity of these formats is due to the use of up to two data storage layers on each side of a DVD disc, and the use of both sides of the disc for data storage.
DVD-5: This format provides for data storage on a single layer and single side of a DVD optical-disc. Total storage capacity for DVD-5 is 4.7 GBytes.
DVD-9: This format provides for data storage on two layers on a single side of a DVD optical-disc. Total storage capacity for DVD-9 is 8.5 GBytes.
DVD-10: This format provides for data storage on a single layer on both sides of a DVD optical-disc. Total storage capacity for DVD-10 is 9.4 GBytes.
DVD-18: This format provides for data storage on two layers on both sides of a DVD optical-disc. Total storage capacity for DVD-18 is 17.0 GBytes.
The ability to use two different layers on a DVD optical-disc provides for a significant increase in the total storage capacity per side. This is accomplished by setting the laser that reads that data off the DVD optical-disc to two different wavelengths, 650 nm and 635 nm. This allows the laser in a DVD playback device to "focus" at two different depths within the DVD optical-disc.
In addition to increasing capacity through the use of multiple layers, DVD lasers use a shorter wavelength than traditional CD-ROM devices. This means that the "pits" and "tracks" that are used to store data on a DVD optical-disc can be much smaller than those used on a CD-ROM.
A traditional CD-ROM uses "pits" that are at least 0.83 microns long, and uses "tracks" that are spaced 1.6 microns apart. A DVD optical-disc uses "pits" that are at least 0.4 microns long and "tracks" that are spaced 0.74 microns apart.
The use of smaller "pits" and closer spaced "tracks" on a DVD optical disc increased the total storage capacity by over 700% compared to a traditional CD-ROM.
Using multiple layers and multiple sides for data storage means that total capacity has been increased to a maximum of 17.0 GBytes. on a DVD optical-disc compared to just 650 Mbytes on a standard CD-ROM, an increase of more than 26 times the capacity.
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