DVD

1. Introducition

DVD：Digital Video Disk，It is a digital video disc or digital video disk, which uses MPEG2 compression technology to store images. Also known as Digital Versatile Disk, it is a digital versatile optical disk that integrates computer technology, optical recording technology, and film and television technology, etc. Its purpose is to meet the demand for storage media with large storage capacity and high performance.

There are two physical sizes: 12cm (4.7") and 8cm (3.1"), both 1.2mm thick, made of two layers of 0.6mm thick base (polycarbonate substrate) bonded together. DVD discs can be single-sided or double-sided. Each side can have 1 or 2 data layers. The capacity of a disc is determined by how much audio accompanies the video, and how the video and audio are compressed. The often cited figure of 133 minutes is not true: a DVD with only one channel can store 160 minutes, and if the compression quality is comparable to that of a VCR, then a single data layer of the DVD can hold almost 9 hours of video and audio.

At an average rate of about 4.7 Mbps (3.5 Mbps for video, 1.2 Mbps for three 5.1 audio tracks), a single-layer DVD can store slightly more than 2 hours of content. A 2-hour movie with three audio tracks will have an average data rate of 5.2 Mbps. A dual-layer DVD with an average data rate of 9.5 Mbps (very close to the 10.08 Mbps limit) can also store a 2-hour movie.If the DVD-Video disc is mainly audio and uses 48kHz/16-bit PCM (slightly better than CD sound quality), then it can store 13 hours of audio (24 hours for dual-layer discs). If you use 64kbps mono Dolby Digital, you can store 160 hours of audio (295 hours for a dual-layer disk).

2. DVD+R VS DVD-R

The DVD-R format was developed by Pioneer in 1997. The format is supported by most common DVD players and is approved by the DVD Forum. DVD+R format was developed by Philips, Sony and its DVD+RW consortium and was introduced in 2002.
Companies that support DVD-R include Pioneer, Toshiba, Hitachi and Panasonic, while companies that support DVD+R include Sony, Philips, Hewlett-Packard, Ricoh and Yamaha.

The main functional difference between DVD-R and DVD + R is the way they determine the position of the laser beam on the disc. dvd-r uses tiny marks on the grooves of the disc (called "table pits") to determine the position of the laser. dvd + R does not have table pits, but instead measures the laser as it moves to the outside of the disc. The "oscillation frequency".

By applying different technologies, DVD+R has better performance than DVD-R in many aspects. For example, DVD+R is ahead of DVD-R in terms of recording quality and speed. therefore, DVD-R discs are usually cheaper than DVD+R format.

Generally speaking, DVD+R is used for storing data and DVD-R is used for storing video. because DVD+R can't be read on some old DVD players, DVD-R seems to be readable on both. If it is on a computer, there is not much difference between the two.

3. Capacity of DVD

CD-ROMs can hold 650 megabits of data, which is 0.64 gigabytes or 680 million bytes. In the following list, SS/DS means Single Side/Double Side, SL/DL/ML means Single Layer/Double Layer/Mixed Layer (mixed layer means one side of the disc has one layer and the other side has two layers), gig means gigabyte (2^30), and BB means billion bytes (10^9).

DVDs are different from CDs in that DVDs can have multiple layers. DVD-5 refers to a single-sided, single-layer DVD, and is the most common DVD. it has a capacity of about 4.7GB, which is close to 5GB, hence the name DVD-5.More than 2 hours of video. Since this product was produced earlier and the technology is more mature, most of the DVD burning discs we see in the market now are of this kind.

DVD-9 refers to a single-sided dual-layer DVD, which is a DVD that contains two information layers on one side, and the combined capacity of the two layers is about 8.5GB. The track spacing of the double layer is about 10% wider than that of the single layer, so the capacity is less than 9.4 GB. the advantage of DVD-9 is that you can store a 120-minute high quality movie on one disc without having to manually change discs in the middle. However, some early DVD players and optical drives do not support DVD-9.

DVD-10 is a double-sided DVD, generally referred to as a double-sided single layer, which, to put it plainly, is two DVD-5s glued together back-to-back to achieve a maximum capacity of 9.4GB，About 4.5 hours video. However, the disadvantage of DVD-10 is that it needs to change the surface manually, and there is no player that supports automatic surface change yet.

DVD-18 is short for double-sided dual-layer disc, just like DVD-10 is made of two DVD-5s, DVD-18 is made of two DVD-9s, with a maximum capacity of about 17GB, Over 8 hours of video，which is the largest DVD disc on the market and extremely rare.

No matter DVD-5 or DVD-9, they are just a branch of DVD, and cannot jump out of the DVD circle, so as long as the newer DVD players can play normally, there is basically no need to worry about compatibility issues.
The common file burning, is to put the file in, what can be, is to use the DVD as a removable hard drive, if burned image files, such as ISO files, is specifically used to burn files, burned with the burning software in the image burning, burned out and sold on the street the same disc!

Tip: It takes an average of 2G bytes to store one hour of video. A CD-ROM can hold about 650 megabytes of data

DVD capacity is larger than CD-ROM for the following reasons.

1. Smaller notch length (~2.08x)
2. Closely spaced data tracks (~2.16x)
3. Slightly larger data area (~1.02x)
4. More efficient channel bit modulation (~1.06x)
5. More efficient error correction (~1.32x)
6. Less segment overhead (~1.06x).
   All this makes a data layer 7 times larger than a CD-ROM.

The capacity of a double-layer disk is slightly less than twice the capacity of a single-layer disk. The laser has to read the inner data layer "through" the outer data layer (at a distance of 20 to 70 microns). To compensate for this, the reference scanning speed is slightly faster (3.84 m/s), compared to 3.49 m/s for the single-layer disk. The longer dots, which are further apart, are easier to read correctly and less susceptible to shaking. Increasing the length means fewer dots per revolution, which results in less data capacity per layer.

Model	Specification	Capacity
DVD-1	(8 cm, SS/SL)	1.36 GB (1.4 BB), about half an hour
DVD-2	(8 cm, SS/DL)	2.48 GB (2.7 BB), approx. 1.3 hours
DVD-3	(8 cm, DS/SL)	2.72 GB (2.9 BB), about 1.4 hours
DVD-4	(8 cm, DS/DL)	4.95 GB (5.3 BB), approx. 2.5 hours
DVD-5	(12 cm, SS/SL)	4.38 GB (4.7 BB)，over 2 hours of video
DVD-9	(12 cm, SS/DL)	7.95 GB (8.5 BB), approx. 4 hours
DVD-10	(12 cm, DS/SL)	8.75 GB (9.4 BB), approx. 4.5 hours
DVD-14	(12 cm, DS/ML)	12.33 GB (13.24 BB), approx. 6.5 hours
DVD-18	(12 cm, DS/DL)	15.90 GB (17 BB), over 8 hours
DVD-R 1.0	(12 cm, SS/SL)	3.68 GB (3.95 BB)
DVD-R 2.0	(12 cm, SS/SL)	4.38 GB (7.4 BB), few DS discs 8.75 GB
DVD-RW 2.0	(12 cm, SS/SL)	4.38 GB (7.4 BB), few DS discs 8.75 GB
DVD-RAM 1.0	(12 cm, SS/SL)	2.40 GB (2.58 BB)
DVD-RAM 1.0	(12 cm, DS/SL)	4.80 GB (5.16 BB)
DVD-RAM 2.0	(12 cm, SS/SL)	4.38 GB (4.7 BB)
DVD-RAM 2.0	(12 cm, DS/SL)	8.75 GB (9.4 BB)
DVD-RAM 2.0	(8 cm, DS/SL)	1.36 GB (1.4 BB)
CD-ROM	(12 cm, SS/SL)	0.635 GB (0.650 BB)
CD-ROM	(8 cm, SS/SL)	0.180 GB (0.194 BB)