Thursday, June 28, 2012

Something about DVD-Video CD

DVD-Video CD

DVD-Video is known as DVD discs.
If CD is developed on the basis of CD-DA and DVD is developed on the basis of DVD-Video. Let's know more about DVD-Video. 


There are two video standards: NTSC and PAL/SECAM.
DVD is compressed with MPEG-2 methods with a changeable compression ratio, an average code rate of 3.5 Mbps, and a maximum code rate of 11 Mbps.

NTSC standard TV 720 pixels / line × 480 lines / frame, 30 frames / sec; PAL standard TV 720 pixels / line × 576 lines / frame, 25 frames / sec. More than 500 horizontal scan lines. And VCD compared, VCD uses MPEG-1 compression, rate fixed at 1.15Mbps, VCD image resolution of 324 × 240,18 million pixels, 240 horizontal scan lines (LD only 430 lines). 


The DVD Audio system is surely the PCM (LPCM), DD (Dolby Digital) DTS and so on. The following are the digital audio types that used in DVD discs.

Technic parameter for the audio code
Required Mode
 NTSC DVD disc should use the following styles:
LPCM 48kHz
Audio compaction mode:
Dolby digit (1-5.1)
 PAL/SECAM DVD disc should use the following methods:
one of the following:
Dolby digit (1-5.1)
MPEG-2 audio
free style
 Dolby Digital surround sound

Linear pulse-code technology is a dual-channel uncompressed PCM signal format used in DVD disc, as detrimental to sound quality without any data compression processing, so get the best sound quality performance. This principle of PCM format with the CD is the same, but DVD has more space and the data read speed advantage, you can use a higher sampling frequency and quantization precision. Now, requiring high-quality of the DVD used 96 Khz/24Bit, so that sound quality is better than DVD discs, CD recording.

2.DD (Dolby Digital)
DD (Dolby Digital) is a kind of patent coding technology developed by Dolby Company. The following is the logo of DD:

Dolby Digital is an advanced perceptual coding technology for transmission and storage of up to five full-bandwidth channels (front left, front right, in the home, left rear, right rear) of information, plus a low frequency sound effects Road. Low-frequency channel because only the following non-full-band bass 120HZ signal Guchang be expressed as 0.1 channel. This is the origin of 5.1. Dolby Digital compression is relatively high, up to 12:1, the space required for its 5.1-channel PCM or even less than the CD encoded in a linear channel space. And Dolby AC-1, AC-2 compared to Dolby Digital is a more effective and more flexible coding system. Dolby Digital, also known as Dolby AC-3, it can provide a range of functions:
1) Mixing function enables the single track, dimensional sound and directional logic and all 5.1 tracks compatible.
2) Transfer to the decoder dynamic range control and dialogue level control information.
3) Set with multiple bit rate mode of operation.

Dolby Digital technology is widely used in film and DVD discs, it was developed in 1998, the new U.S. high-definition television system (ATSC) audio standards, and in 1999 became the European digital TV standards (DVB) an optional audio standard. DVD disc, the Dolby Digital can be a single channel, dual channel; it can be 5.1, which according to the requirements of producers to set up.

3. DTS
DTS(Digital Theater Systems)derived from the cinema sound system, the United States DTS TECHNOLOGY developed by a digital stereo surround sound formats. The figure is a DTS logo:

DTS Coding can fit for a wider range of bit scope, especially for 20 bit digital audio (44.1 KHz, 48 KHz); it provides the correspondent definition and diaphaneity. The working principle of the encoding key is to filter the digital audio where the objective redundant information, so as to achieve bit rate reduction purposes. DTS decoding the main features of work in high-bit rate, decoding operation using a shorter buffer, while taking advantage of less complex programs to restore the original 6-channel 20-bit audio signals. DTS uses compression CAC structure is different from Dolby Digital compression method, the typical compression ratio of 3:1, only a quarter of Dolby Digital. Secondly, DTS to 96KHz sampling frequency of 48KHz Dolby Digital double, and easy data transfer rates of up to 1536Kbps, higher than 448Kbps Dolby Digital 3-fold, DTS multi-channel processing are also all channel to go through filtering, sub-frequency spectrum analysis, re-quantitative techniques for processing, and then sent to the "common bit group" within the re-treatment, so that each channel has a good full-range frequency response. Thus, DTS format of various aspects of technical design, not only help to improve the purity of the sound, but also a broader sense of space.

Similarly with 5.1 channel, DTS and DD 5.1 has a different figure methods, that is to compress the 5.1 track with different methods. Dolby Digital 5.1 will compress the same data much smaller so that it can take the minimum space. But the DTS does not aim for the ability of compaction. So it has much more chances to keep more information, if properly handled, it can indeed offer a better performance.

No matter DD 5.1 or DTS5.0, the position of sound box will like below:


Picture has two formats 4:3 and 16:9. In the format of 4:3, there are normal, PS, LB three modes. The following is the figure of 4:3, 16:9, PS and LB.


Recording image of disc 4:3

If the recording image of DVD discs is using 4:3 formats, the origin image shall be displayed no matter on 4:3 screen or 16:9 screen. The only difference is that there is a blank or shadow stripe on the left and right side of 16:9 screen.

If the DVD disc images are recorded on 16:9 format, then using 16:9 screen playback can reproduce the original image, but with the 4:3 screen during playback, different models have different effects. In the normal mode, the screen displays the image of the panorama, but it was compressed in the horizontal direction; in PS mode, the screen shows the middle part of the image, but to delete the image left and right sides; in LB mode, the screen shows the complete picture, but from top to bottom have a blank tape (filament).

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