CD: pure music

VCD: primary video disc

DVD: high-definition video disc

EVD: high-definition digital video< /p>

MPEG4: Compress high-density film and television discs

MP3: Compress pure music

DVD has high density, high image quality, high sound quality, high compatibility and high reliability Features. High density: Both DVD and CD discs have a diameter of 120mm, but the CD has a capacity of 680MB, which can only store 74 minutes of VHS quality dynamic video images, while a single-sided single-layer DVD recording layer has a capacity of 4.7GB. If it is close to The average data rate required for broadcast television image quality is 4.69Mbps, which can store an entire movie of 133 minutes and 20 seconds. Double-sided double-layer discs have a capacity of up to 17GB and can hold 4 movies on a single disc. This requires the use of more advanced technical means in DVD to increase the information recording density, thereby increasing the disk capacity. The following table lists several technical means used to increase the recording density of optical discs. Technical means CD/VCD DVD Mirror numerical aperture NA 0.45 0.6 Error correction coding redundancy 31% 15.4% Channel code modulation method 8/17 modulation 8/16 modulation Laser wavelength λ 780nm 650nm/635nm Spot diameter 1.74μm 1.08μm Track pitch 1.6 μm 0.74μm Minimum pit length 0.83μm 0.4μm Pit width 0.6μm 0.4μm Capacity 650MB 4.7GB High image quality: DVD adopts the internationally accepted moving image compression standard MPEG-2 (ISO/IEC13818), and its system code stream transmits data The rate is variable (1~10.7Mbps); at this stage, DVD-Video products use the main level standard MP@ML (that is, NTSC standard TV 720 pixels/line × 576 lines/frame) among the 11 standards of MPEG-2 , 30 frames/second; PAL standard TV 720 pixels/line × 488 lines/frame, 25 frames/second, maximum data transmission rate is 15Mbps), reaching broadcast-level TV image quality (its horizontal resolution is more than 500 lines). To achieve higher definition image quality, you can also choose the corresponding advanced specifications in MPEG-2. The DVD system code stream consists of the main video code stream (MPEG-2/MPEG-1 compressed code stream), sub-image code stream (up to 32 code streams can be recorded and played, used for 32 types of text movie dialogue and karaoke subtitle display) and It consists of three parts: audio code streams (can record and play up to 8 code streams, supports 8 language sounds). The maximum data rate of the entire system code stream can reach 10.08Mbps. DVD also has new features such as multiple endings (enjoying different storyline developments), multiple angles (viewing images from 9 angles), zoom and parental control (cutting out scenes inappropriate for children). There are three ways to choose the aspect ratio of the picture: panoramic scan, 4:3 normal screen and 16:9 wide screen mode. PCM Dolby AC-3 Audio Sampling frequency 48KHz/96KHz 48KHz 48KHz Sampling accuracy 16/20/24bit Compressed data Compressed data data rate 768Kbps ~ Minimum 32Kbps Main stream: Minimum 64Kbps 2.304Mbps Maximum 48Kbps Maximum 384Kbps One audio stream 1 5.1 7.1 Number of channels in Maximum number of audio streams 2 to 8 Maximum 8 Maximum 8 High sound quality: DVD has 8 (7.1) independent audio streams, which is enough to achieve digital surround three-dimensional high-fidelity sound effects. DVD standard regulations: For NTSC TV formats (such as the United States and Japan), it is mandatory to use Dolby AC-3 and/or linear PCM audio systems; for PAL TV formats (such as Europe and China), it is mandatory to use MPEG audio format and/or Or linear PCM audio system. Table 3 gives the technical parameters of three audio systems. In 1992, Dolby Laboratories in the United States released the AC-3 digital surround sound system, with 6 completely independent channels (left, right, center, left surround, right surround and subwoofer, referred to as 5.1 channels) and full-band (~20KHz) high-precision and realistic sound field, producing very good on-site digital surround high-fidelity sound effects. High compatibility: DVD players, DVD record players and DVD-ROM/R/RAM can all play CD discs; DVD players and DVD-ROM/R/RAM can all play back VCD discs; DVD-ROM/R/RAM can also read CD-ROM disk. High reliability: DVD uses RS-PC (Reed Solomon Product Code) error correction coding method and 8/16 signal modulation method to ensure reliable data reading. The error correction code (ECC) block length is 16 recording sector length (38688 bytes), corresponding to the length of 82.5344mm on the optical track; if the original bit error rate is 10-3, after error correction, the bit error rate can be less than 10 -20, which is far lower than the required bit error rate of 10-12 for computers.

In order to effectively prevent software from being copied, in July 1996, with the active participation of the Motion Picture Association of America, 12 home appliance and computer companies including Toshiba and Sony reached an agreement on DVD software copyright and anti-piracy issues. unanimous agreement. In October 1996, the DVD Technology Federation composed of various parties announced the garbled technology used in DVD software and hardware and measures to distribute software according to six regional code partitions, achieving software copyright protection and reliable use.