|Media type||Optical disc|
|Encoding||MPEG-1 video + audio|
|Capacity||Up to 800 MB|
|Read mechanism||780 nm wavelength semiconductor laser|
|Developed by||Philips, Sony, Panasonic, JVC|
|Usage||audio and video storage|
Before the advent of DVD and Blu-ray, the Video CD (abbreviated as VCD, and also known as Compact Disc digital video) became the first format for distributing films on standard 120 mm (4.7 in) optical discs.
The format is a standard digital format for storing video on a compact disc. VCDs are playable in dedicated VCD players, most DVD and Blu-ray Disc players, personal computers, and some video game consoles.
Although they have been superseded by other mediums, VCDs continue to be retailed as a low-cost video format.
- 1 Brief history
- 2 Technical specifications
- 3 Similar formats
- 4 Adoption
- 5 Compared with VHS
- 6 Compared with DVD
- 7 Hardware and software support
- 8 See also
- 9 References
- 10 External links
In 1979, Philips introduced the optical LaserDisc, which was about 30 cm (12 in) in diameter. This disc could hold an hour of analog video along with digital audio on each side. The Laserdisc provided picture quality nearly double that of VHS tape and audio quality far superior to VHS. By 1986 in the U.S. Laserdiscs were beginning to develop a small but loyal following from people who wanted better quality than VHS tape. However, Laserdiscs were always overshadowed by VHS because of their high price and lack of recording abilities.
Philips later teamed up with Sony to develop a new type of disc, the compact disc or CD. Introduced in 1982 in Japan (1983 in the U.S.), the CD is about 120 mm (4.7 in) in diameter, and is single-sided. The format was initially designed to store digitized sound and proved to be a success in the music industry.
A few years later, Philips decided to give CDs the ability to produce video, just like its Laserdisc counterpart. This led to the creation of CD Video (CD-V) in 1987. However, the disc's small size significantly impeded the ability to store analog video; thus only 5 minutes of picture information could fit on the disc's surface (despite the fact that the audio was digital). Therefore CD-V distribution was limited to featuring music videos.
By the early 1990s engineers were able to digitize and compress video signals, greatly improving storage efficiency. Because this new format could hold 83 minutes of audio and video, releasing movies on compact discs finally became a reality. Extra capacity was obtained by sacrificing the error correction (it was believed that minor errors in the datastream would go unnoticed by the viewer). This format was named Video CD or VCD.
VCD enjoyed a brief period of success, with a few major feature films being released in the format (usually as a 2 disc set). However the introduction of the CD-R disc and associated recorders stopped the release of feature films in their tracks because the VCD format had no means of preventing unauthorized (and perfect) copies from being made. However, VCDs are still being released in several countries in Asia, but they recently had means of copy-protection.
The development of more sophisticated, higher capacity optical disc formats yielded the DVD format, released only a few years later with a copy protection mechanism. DVD players use lasers that are of shorter wavelength than those used on CDs, allowing the recorded pits to be smaller, so that more information can be stored. The DVD was so successful that it eventually pushed VHS out of the video market once suitable recorders became widely available. Nevertheless, VCDs made considerable inroads into developing nations, where they are still in use today.
Video CDs comply with the CD-i Bridge format, and are authored using tracks in CD-ROM XA mode. The first track of a VCD is in CD-ROM XA Mode 2 Form 1, and stores metadata and menu information inside an ISO 9660 filesystem. This track may also contain other non-essential files, and is shown by operating systems when loading the disc. This track can be absent from a VCD, which would still work but would not allow it to be properly displayed in computers.
The rest of the tracks are usually in CD-ROM XA Mode 2 Form 2 and contain video and audio multiplexed in an MPEG program stream (MPEG-PS) container, but CD audio tracks are also allowed. Using Mode 2 Form 2 allows roughly 800 megabytes of VCD data to be stored on one 80 minute CD (versus 700 megabytes when using CD-ROM Mode 1). This is achieved by sacrificing the error correction redundancy present in Mode 1. It was considered that small errors in the video and audio stream pass largely unnoticed. This, combined with the net bitrate of VCD video and audio, means that almost exactly 80 minutes of VCD content can be stored on an 80 minute CD, 74 minutes of VCD content on a 74 minute CD, and so on. This was done in part to ensure compatibility with existing CD drive technology, specifically the earliest "1x" speed CD drives.
- Codec: MPEG-1
- Aspect Ratio:
- Bitrate: 1,150 kilobits per second
- Rate Control: constant bitrate
Although many DVD video players support playback of VCDs, VCD video is only compatible with the DVD-Video standard if encoded at 29.97 frames per second or 25 frames per second.
The 352x240 and 352x288 (or SIF) resolutions were chosen because it is half the horizontal and vertical resolution of NTSC video, and half the horizontal resolution of PAL (the vertical resolution of PAL already being half of the 576 active lines). This is approximately half the resolution of an analog VHS tape which is ~330 horizontal and 480 vertical (NTSC) or 330x576 (PAL).
- Codec: MPEG-1 Audio Layer II
- Sample Frequency: 44,100 hertz (44.1 kHz)
- Output: Dual channel or stereo
- Bitrate: 224 kilobits per second
- Rate Control: Constant bitrate
As with most CD-based formats, VCD audio is incompatible with the DVD-Video standard due to a difference in sampling frequency; DVDs require 48 kHz, whereas VCDs use 44.1 kHz.
Advantages of compression
By compressing both the video and audio streams, a VCD is able to hold 74 minutes of picture and sound information, nearly the same duration as a standard 74 minute audio CD. The MPEG-1 compression used records mostly the differences between successive video frames, rather than write out each frame individually. Similarly, the audio frequency range is limited to those sounds most clearly heard by the human ear.
The VCD standard also features the option of DVD-quality still images/slide shows with audio, at resolutions of 704x480 (NTSC) or 704x576 (PAL/SECAM). Version 2.0 also adds the playback control (PBC), featuring a simple menu like DVD-video.
An example of the software control chart (taken from Flower And Snake disc 1 of 3) including menu commands found in the configuration volume as "CDI_VCD.CFG"
CD-i Digital Video
Shortly before the advent of White Book VCD, Philips started releasing movies in the Green Book CD-i format, calling the subformat CD-i Digital Video (CD-i DV). While these used a similar format (MPEG-1), due to minor differences between the standards these discs are not compatible with VCD players. Philips' CD-i players with the Full Motion Video MPEG-1 decoder cartridge would play both formats. Only a few CD-i DV titles were released before the company switched to the current VCD format for publishing movies.
XVCD (eXtended Video CD) is the name generally given to any format that stores MPEG-1 video on a compact disc in CD-ROM XA Mode 2 Form 2, but does not strictly follow the VCD standard in terms of the encoding of the video or audio.
A normal VCD is encoded to MPEG-1 at a constant bit rate (CBR), so all scenes are required to use exactly the same data rate, regardless of complexity. However, video on an XVCD is typically encoded at a variable bit rate (VBR), so complex scenes can use a much higher data rate for a short time, while simpler scenes will use lower data rates. Some XVCDs use lower bitrates in order to fit longer videos onto the disc, while others use higher bitrates to improve quality. MPEG-2 may be used instead of MPEG-1.
To further reduce the data rate without significantly reducing quality, the size of the GOP can be increased, a different MPEG-1 quantization matrix can be used, the maximum data rate can be exceeded, and the bit rate of the MP2 audio can be reduced (or even the use of MP3 audio instead of MP2 audio). These changes can be advantageous for those who want to either maximize video quality, or use fewer discs.
KVCD (K Video Compression Dynamics) is an XVCD variant that requires the use of a proprietary quantization matrix, available for non-commercial use. KVCD is notable because the specification recommends a non-standard resolution of 528x480 or 528x576. KVCDs encoded at this resolution are only playable by computers with CD-ROM drives, and a small number of DVD players.
DVCD or Double VCD is a method to accommodate longer videos on a CD. A non-standard CD is overburned to include up to 100 minutes of video. However, some CD-ROM drives and players have problems reading these CDs, mostly because the groove spacing is outside specifications and the player's laser servo is unable to track it.
Super Video CD is a format intended to be the successor of VCD, offering better quality of image and sound.
In North America
The advent of recordable CDs, inexpensive recorders, and compatible DVD players spurred VCD acceptance in the US in the late 1990s and early 2000s. However, DVD burners and DVD-Video recorders were available by that time, and equipment and media costs for making DVD-Video fell rapidly. DVD-Video, with its longer run time and much higher quality, quickly overshadowed VCD in areas that could afford it. In addition many early DVD players could not read recordable (CD-R) media, and this limited the compatibility of home-made VCDs. Almost every modern stand-alone DVD-Video player can play VCDs burned on recordable media.
It is reported the first home VCD player was made in Hefei, China in 1993.The VCD format was very popular throughout Asia (except Japan and South Korea) in the late 1990s through the 2000s, with 8 million VCD players sold in China in 1997 alone, and more than half of all Chinese households owning at least one VCD player by 2005. However, popularity has declined over the years, as the number of Hong Kong factories that produced VCDs dropped from 98 in 1999 to 26 in 2012.
This popularity is, in part, because most households did not already own VHS players when VCDs were introduced, the low price of the players, their tolerance of high humidity (a notable problem for VCRs), easy storage and maintenance, and the lower-cost media. Western sources have cited pirated content as a principal incentive for VCD player ownership.
VCDs are often produced and sold in Asian countries and regions, such as Mainland China, Taiwan, Hong Kong, Singapore, Malaysia, Thailand, Burma, Indonesia, Philippines, Vietnam, India, Pakistan and Bangladesh. In many Asian countries, major Hollywood studios (and Asian home video distributors) have licensed companies to officially produce and distribute the VCDs, such as MCA Home Video in Pakistan, Intercontinental Video Ltd. of Hong Kong, Sunny Video in Malaysia, Vision in Indonesia, CVD International and Pacific Marketing and Entertainment Group in Thailand, Excel Home Video in India, Berjaya-HVN and InnoForm Media in both Malaysia and Singapore, Scorpio East Entertainment in Singapore, as well as VIVA Video, Magnavision Home Video, and C-Interactive Digital Entertainment in the Philippines. Legal Video CDs can often be found in established video stores and major book outlets in most Asian countries. They are typically packaged in jewel cases like commercial CDs, though higher-profile films may be released in keep cases. The consumer should always check for the VCD or DVD logo so as to avoid purchasing the wrong format.
In Asia, the use of VCDs as carriers for karaoke music is very common. One channel would feature a mono track with music and singing, another channel a pure instrumental version for karaoke singing. Prior to this, karaoke music was carried on laserdiscs.
VCD's growth has slowed in areas that can afford DVD-Video, which offers most of the same advantages, as well as better picture quality (higher resolution with fewer digital compression artifacts) due to its larger storage capacity. However, VCD has simultaneously seen significant new growth in emerging economies like India, Indonesia, South America and Africa as a low-cost alternative to DVD. As of 2004, the worldwide popularity of VCD was increasing.
Compared with VHS
Overall picture quality is intended to be comparable to VHS video. Poorly compressed VCD video can sometimes be of lower quality than VHS video, for example exhibiting VCD block artifacts (rather than the analog noise seen in VHS sources), but does not deteriorate further with each use. While both formats need fast-forwarding to find certain scenes, rewinding to the beginning upon reaching the end is not required in VCD. The resolution is just slightly below that of common VHS resolution.
Though technically superior to tape-based mediums, VCDs have a few minor flaws. Videos in the format do not come with closed caption (on-screen text to aid viewers with hearing problems). When watching a film that exceeds 74 minutes, which is the maximum video capacity of one disc, a viewer would have to change the disc upon reaching half-way (unless the discs are played on a VCD changer that could hold multiple discs as well as playing them automatically in succession), whereas a single VHS can hold 3½ hours of continuous video (as of 2014, 10 hour VHS tapes are available).
Compared with DVD
When playing a DVD, the viewer is brought to a main menu which gives them options (watch the feature film, view "deleted scenes", play some special applications, etc.). VCDs are usually straightforward, playing them often goes directly to the video with extras (mostly trailers and commercials) taking place before or after it.
Subtitles are found on many Asian VCDs but cannot be removed, unlike DVDs. The subtitles are embedded on the video during the encoding process. It's not uncommon to find a VCD with subtitles for two languages.
Though the VCD technology can support it, most films carried on VCDs do not contain chapters, requiring the viewer to fast-forward to resume the program after playback has been stopped. This is mostly because VCD technology is able to start playback at a chapter point but there is nothing to signal the player that the chapter has changed during a program. This can be confusing for the user as the player will indicate that it is still playing chapter 1 when it has played through to chapter 2 or later. Pressing the Next button would cause playback from the beginning of chapter 2. However, preview material is sometimes stored in a separate chapter, followed by a single chapter for the film.
VCDs are often bilingual. Because they feature stereo audio, disc players have an option to play only the left or right audio channel. For example, ERA of Hong Kong's release of the animated film The Iron Giant features English on the left audio channel and Cantonese on the right; more commonly Hong Kong VCDs will feature Mandarin on one channel and Cantonese on the other. This is similar to selecting a language track on a DVD, except it's limited to 2 languages, due to there being only two audio channels (left and right). The audio track effectively becomes monaural.
VCD's most noticeable disadvantage compared to DVD is image quality, due both to the more aggressive compression necessary to fit video into such a small capacity as well as the compression method used. Additionally, VCDs are available only in stereo, while DVDs are capable of six channels of discrete surround sound. The audio compression of VCDs also suffers from not being able to pull off the Haas effect for matrixed surround sound.
Hardware and software support
Video CDs are not popular in the US, Canada and Europe, so its support is limited among mainstream software. Windows Media Player prior to version 9 and QuickTime Player do not support playing VCD directly, though they can play the .DAT files (stored under \MPEGAV for video and audio data) reliably, and plugins were available. Windows Vista added native support of VCD along with DVD-Video and can launch the preferred application upon insertion. The disc format is also supported using Windows Media Player Classic variations and VLC Media Player both support VCDs natively.
Most DVD players are compatible with VCDs, and VCD-only players are available throughout Asia, and online through many shopping sites. Older Blu-ray and HD-DVD players also retained support, as do CBHD players as well. However, most current Blu-ray players and the Sony PlayStation 3 cannot play VCDs; this is because while they have backwards playback compatibility with the DVD standard, these player can not read VCD data because the player software does not have support for MPEG-1 video and audio.
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