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The China Video Disc (or CVD) standard is a CD-based MPEG-2 audio and video format developed in 1997. It is almost identical to the SVCD standard, the only technical difference being a lower video resolution.

Technical specifications

On a technical basis the CVD standard is all but identical to the SVCD standard. The only difference between the two formats is the video resolution: SVCDs require 480x576 (PAL/SECAM) or 480x480 (NTSC) resolution video, whereas CVDs use 352x576 (PAL/SECAM) or 352x480 (NTSC) resolution video. All other technical aspects of the CVD standard are identical to those of the SVCD standard.

Video

Codec : MPEG-2
Resolution :
o NTSC: 352x480
o PAL/SECAM: 352x576
Aspect Ratio : 4:3
Framerate :
o NTSC: 29.97 or 23.976 frames per second
o PAL/SECAM: 25 frames per second
Bitrate : Up to 2.6 Megabits (2,600 kilobits) per second
o Rate Control: Constant or variable bitrate

Interlaced video is supported (though not required) for CVD video, excepting any video at 23.976 frames per second, as it must use 3:2 pulldown.

The CVD video standard is almost completely compatible with the DVD-Video standard. However, the CVD standard does not specify any limits on GOP structure, and as such it is possible to encode CVD video with a GOP size larger than DVD-Video's 64 frame-per-GOP limit. In practice this is highly uncommon; most commercially produced CVD video uses a 12 or 15 frame GOP structure, which is compatible with the DVD-Video standard.

Audio

Codec : MPEG-1 Audio Layer II
Frequency : 44,100 Hertz (44.1 kHz)
Output : Monaural, Dual Channel, or Stereo
Bitrate : Certain bitrates between 32 and 384 kilobits per second, inclusive
o Rate Control: Constant bitrate

As with most CD-based video formats, CVD audio is incompatible with the DVD-Video standard due to the difference in frequency; DVDs require 48 kHz, whereas CVDs use 44.1 kHz.

Additional Features

Support for features such as karaoke, selectable subtitles, two selectable audio tracks, and DVD-quality slide shows.

Advantages/Disadvantages to SVCD

Though the lower resolution of the CVD standard brings with it less detailed video than the SVCD standard, it also provides certain advantages. Most obvious are the space requirements for 'decent quality' video, as the lower resolution allows the bitrate to be reduced significantly more while keeping the number of 'compression errors', such as MPEG block artifacts, to a minimal level. Other advantages primarily center around the DVD support for the resolution; while CVD standard video is also DVD-compatible, SVCD standard video is not. Initially this is only useful for transferring CVD content to DVD, as the video does not have to be transcoded and can avoid the quality loss which would result. (Though the audio must be transcoded, as DVDs require 48 kHz audio rather than the 44.1 kHz audio used on CVDs) Additionally, CVDs do not suffer from certain playback issues faced by SVCDs due to limitations present in many DVD players. These issues are mostly due to 'foldover' or aliasing problems encountered when the DVD player resizes the video as it plays it. While SVCDs are frequently affected by this issue CVDs are not, as the resizing algorithms used by DVD players are almost always optimized with valid DVD resolutions (such as the CVD resolution) in mind.

The major disadvantages of the CVD standard, aside from the lower resolution, are primarily compatibility issues. While almost all PAL DVD players which are listed as 'SVCD compatible' must also support the CVD standard, DVD players sold in the United States have no such requirement. Though no solid figures exist, it has been estimated that roughly a quarter of those DVD players sold in the United States which are 'SVCD compatible' do not support the CVD standard.

History of development

As the name indicates, the CVD standard originated in China. It was developed by C-Cube Systems as part of a late 1990s Chinese government-sponsored effort to create a next-generation CD-based video standard. It was the first of three competing formats (the others being SVCD and HQ-VCD) to be released into the Chinese market. This early release, which quickly established a significant CVD customer base, eventually prompted the Chinese government to force a compromise between the competing standards. Both the SVCD and CVD standards were combined into one composite standard known as Chaoji Video CD, (though it is still often called 'SVCD') which was adopted by the Chinese government as the 'official' next-generation video disc standard.

Wikipedia information about China Video Disc
. This article is licensed under the GNU Free Documentation License . It uses material from the Wikipedia article 'China Video Disc'








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