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Video to DVD & CD: Video disc technology
Traditionally the most common distribution of video material has been on VHS tape. Over the last few years video discs have gained popularity as a means of distributing video either on CD ROM or DVD.
CD ROM
In 1993 Philips and JVC agreed a specification for video on compact disc - the VCD "white book standard", enabling video to be played on a stand-alone Video Compact Disc Player or a personal computer equipped with a CD ROM, sound card and suitable software. All modern computers should have this capability. (Don't expect a ten year old pc to work too well though).
In order to squeeze up to 70 minutes of video and audio onto the VCD the video is compressed into a digital format known as MPEG-1. The picture quality roughly equates to VHS. Subjectively the picture is slightly softer but less noisy and without dropouts (it either works or it doesn't) but a noticeable effect is a tendency for the picture to become blocky or grainy on movement, mixes or fades due to the high digital compression used.
If the CD is to be used only on a computer it need not conform to the "white book standard". Less compression (increasing the bit rate) will reduce the blockiness at the expense of running time (though some older computers may baulk at this and produce jerky pictures) and lowering the bit rate will allow more running time but movement can become very blocky.
The level of compression used will be made during the production of the CD and cannot be adjusted during playback so it is important that the correct choice is made depending on the intended use of the CD.
DVD
The Digital Versatile Disc - DVD although looking outwardly similar to the Compact Disc can hold far more data allowing 2+ hours of broadcast quality pictures to be stored.
MPEG-2 compression is used and although having to conform to certain parameters the bit rate can be set during the encoding process to allow for running time versus quality and will play on both a stand-alone DVD player or suitably equipped modern personal computer. (Microsoft Windows Media Player does not have the decoding software to play MPEG-2 as standard but later machines usually have third party software installed. Suitable software DVD players can easily be cheaply purchased or downloaded from the web.)
The DVD system allows far more interactive extras to be added than VCD. Front end menus can be created and chapter points can be added enabling the viewer to instantly jump to various parts of the video. The DVD system can also support multi channel dolby sound tracks, subtitles and interactive games.
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