About DVD

DVD, which stands for Digital Video Disc or Digital Versatile Disc, is the next generation of optical disc storage technology. It is essentially a larger and faster disc that can hold video as well as audio and computer data. DVD aims to encompass home entertainment, computer, and business information with a single digital format, eventually replacing audio CD, videotape, VCD, laser discs, and CD-ROM.

DVD has widespread support from all major electronics companies, all major computer hardware companies, and about half of the major movie and music studios.

DVD Specification is divided into the following five categories.

1.DVD-ROM
DVD-ROM is like a larger CD-ROM, allowing for data and interactive material as well as video and audio. A DVD-ROM drive has to be installed in order to play DVD-ROM titles.

2. DVD-Video
DVD-Video is a movie format which features MPEG2 compressed streams providing about 133 minutes of high-quality video per side according to compression rates. DVD-Video also supports Dolby Digital stereo/surround audio, which offers five discrete channels of high-quality audio plus a subwoofer. A DVD-Video disc can be played both on DVD-ROM drives and standalone home DVD-players.

3. DVD-Audio
DVD-Audio is a next-generation music format that provides higher sampling rate than music CDs. There are two competing standards currently. One is the WG-4 specification from DVD Consortium and the other is Super Audio CD from Sony and Philips. Since there is no formal specification or industrial standard that has been finalized, no DVD-Audio player is available on the market at present time.

4.DVD-R
DVD-R is a write-once version used for creating masters. The capacity of DVD-R is up to 4.7GB currently and it is also readable by both DVD-ROM drives and DVD-players.

5.DVD-RAM
DVD-RAM is the official re-writable DVD sanctioned by DVD Forum. The capacity of DVD-RAM is up to 4.7GB currently but it is only readable by DVD-RAM drives instead of DVD-ROM drives or DVD-players.

A DVD disc can consist of up to four pressed data layers, two on each side, for a total capacity of 17.08GB on a 12cm disc, or 5.32 GB on an 8cm disc. The most likely version for the near future will be single layer single sided 12cm discs with a capacity of 4.70GB. Detailed DVD configurations are categorized as follows.

4.7GB (Single sided, Single Layer), referred to as DVD 5
8.5GB (Single sided, Dual Layer), referred to as DVD 9
9.4GB (Double sided, Single Layer), referred to as DVD 10
17.0GB (Double sided, Dual Layer), referred to as DVD 18

Each layer of data on a DVD disc will allow up to approximately 133 minutes of full motion MPEG2 video.

(1) Features of DVD-Video:

Over 2 hours of high-quality digital video (over 8hrs on a double-sided, dual-layer disc)
Support widescreen movies on standard or widescreen TVs (4:3 and 16:9 aspect ratios)
Up to 8 tracks of digital audio, each with as many as 8 channels
Up to 32 subtitle/Karaoke tracks
Up to 9 camera angles (different viewpoints can be selected during playbacks)
Menus and simple interactive features
Automatic "seamless" branching of video (for multiple story lines or ratings on one disc)

A table of comparison between DVD, VCD and LD is provided as follows.

----------------------------------	DVD-Video	Video CD	LD
Compression Method	MPEG II	MPEG I	Analog
Resolution	720x480 Pixels	324x240 Pixels	N/A
Horizontal Resolution	Over 480	240	430
Frequency	30 frames/sec 60 filters/sec	30 frames/sec	30 frames/sec
Coding Method	VBR/CBR(Variable bit rate/Constant bit rate)	CBR	N/A
Max. Bit Rate	10.08 Mbps	1.15 Mbps	N/A
Avg. Bit Rate	3.5 Mbps	1.15 Mbps	N/A
Avg. Compression Ratio	About 1/40	About 1/100	N/A
Audio compression	Dolby Digital (AC-3)	MPEG I	N/A
Video Length	133 minutes (single sided, single-layer)480 minutes (double-sided, dual-layer)	74 minutes	60 minutes (Single sided)120 minutes (double sided)
Video Specification	Various kinds of specification	N/A	N/A
Subtitle	Up to 32 subtitles	N/A	N/A
Source: Research project from ITRI.

(2) Video features of DVD-Video

MPEG2 video was originally developed by MPEG organization. It uses I-B-P frame structure to compress data. The sequence of frame structure is I-B-B-P-B-B-P-B-B-P-B-B-P-B-B-I and continue to repeat 15 times to compose what is so-called GOP (Group of Picture). Compressed MPEG2 video transforms to GOP data and either of VBR or CBR method can be used. MPEG2 is used for applications requiring high quality video such as satellite broadcast, HDTV, and telephone interactive video. MPEG2 encoding can provide video up to 60 fields per second with a resolution of 720x480 and a variable bit rate up to 9.8 Mbps. There may be noticeable artifacts (block or fuzziness) at 3Mbps average bit rate. At a much higher bit rate, there will be no perceived difference in video quality.

(3) Audio features of DVD-Video

DVD specification allows for up to eight streams of digital audio to be stored on the disc. It supports several forms as standards. Dolby Digital (Surround AC-3) is the audio compression standard for DVD audio in USA and Japan. MPEG2 audio is the standard in Europe. Both audio compression techniques are similar in certain ways such as supporting more channels/speakers than the other methods. DTS and PCM are also encoding audio formats that are supported by DVD.

Dolby Digital AC-3: It provides six separate full bandwidth channels of sound. Full bandwidth means the five main channels range from 3Hz to 20000Hz in comparioson to Dolby Surround Pro Logi's bandwidth range of 100Hz to 7000Hz. Dolby Digital AC-3 for DVD has a sampling frequency of 48KHz and has at least 20 bit dynamic range digital audio channels. The DVD standard specifies audio sectors ehich have an average data rate of 384 Kbps for each one.
MPEG2 audio: The MPEG2 audio standard has the same six channels setup as Dolby Digital AC-3, but it also has the capability of using a left-center speaker and a right-center speaker which make up a 7.1 channel configuration. Although the bit rate of 384 kb/s is sufficient to code the 5.1 channels, the peak bit rate is sometimes needs to extend to 576 kbps for more complex scenes. MPEG2 has a sampling frequency of 48KHz and at least 20 compressed bits per sample.
Linear PCM: The PCM audio available for the DVD format ranges from mono to eight channels and can be 48 KHz (24 bits up to four channels, 20 bits to six and 16 bits to eight) or 96 KHz (24 bits for stereo, 20 bits for three, and 16 bits for four)
DTS (Digital Theater System): DTS is an audio encoding format similar to Dolby Digital. Since DTS has lower compression level, it seems to sound better than Dolby Digital.

Region code is implemented to prevent users from playing DVD titles before they are actually released in certain countries and areas. Besides, regional coding is optional and DVD discs without codes at all will be played on any DVD player in any country. The following drawing and summary represents codes and their corresponding region.

Region 1 --> North America, Canada
Region 2 --> Japan, Europe, The Middle East, Egypt, South Africa, Greenland
Region 3 --> Southeast Asia (including Hong-Kong)
Region 4 --> Central/South America, Australia, New Zealand, Carribean
Region 5 --> Africa, Northwest Asia (including Korea), Soviet Union
Region 6 --> China
Region 7 --> Reserved
Region 8 --> Special international venues (airplanes, cruise ships, etc.)

It should be noticed that DVD discs may have multiple regional codes inserted, in which they can only be played in those respective areas.

The so-called Premastering engineering refers to divide the Video, Audio, data which are desired to be recorded into a DVD, in accordance with DVD specification, through signal processing, Format Transferring engineering, into two major parts of Encoder and Authoring. The following drawing indicates the Premastering engineering block diagram.

Premastering Engineering Block Diagram; Data Resource: www.dvdinsider.com

Encoder Engineering
Video material through Video Encoder of MPEG2 can perform image encoding in Variable bit rate (VBR) manner; while Audio through Audio Encoder can perform encoding in the forms of Dolby AC-3 (NTSC system), MPEG Audio (PAL system) or Linear PCM, etc.

Authoring Engineering
Input the encoded Video and Audio into logic format by means of Authoring software, and perform file structure allocation according to DVD specification. At this time, such required information in display as subtitle, menu graphics, etc. shall be jointly input. After completion of this part, it is saved into one Package, referred to as "Finished Package". Finished Package is normally saved in the form of DLT or digital disc. At this time, Proofing can be conducted through Emulation, to ensure the correctness and quality of encoding and authoring process.