VHS The arrival of the VHS (Video Home System) in 1976 marked the emergence of this field in the world. The video cassette became a house-hold name and was the preferred medium for home entertainment in the 70s, 80s, and in the early 90s. The VHS was capable of storing both audio and video formats of data. It provides a 240 line resolution quality. The VHS tape was capable of playing all the analog TV signals of its time. The signals in use at the time were NTSC, PAL, PAL-M, SECAM, and MESECAM. The VCRs were able to handle only signals specific to the country they were sold in. Based on the tape speeds, the maximum play time for a 430m tape is about 3.5 hours for NTSC and five hours for PAL at SP (standard) quality. This is one of the poorest quality video formats. Due to the size of the video cassette, correspondingly the VHS recording camera was also big and cumbersome. There was a limitation on the size of the data that could be stored. The VHS-C or VHS-Compact was designed with a 8mm tape size. Although it had the same half inch magnetic tape and 240 line resolution, it allowed for the video camera to be lighter, smaller and more convenient. This 8mm tape is however not compatible with the standard VCRs and cannot be played directly on them. To improve on the VHS system, the S-VHS was designed as an improved analog standard, followed by the D-VHS that records digital quality video onto a VHS cassette. The W-VHS was designed to produce a high definition video. Even with all these advances, the quality of video and audio had much to ask for. VCD In keeping with the consumers demand of higher quality home entertainment systems, the Compact Disc (CD) was formulated in 1988 by Sony and Philips. The VCD (Video Compact Disc) format was launched in 1993 by Masushita, Sony, Philips, and JVC. Using the MPEG-1 compression technology, it was capable of holding a 74 minute video of VHS quality and a CD-quality sound. Then the better quality SVCD (Super Video Compact Disc) was introduced, that used the MPEG-2 compression format, but its playing time was diminished to 35 minutes. The VCDs were not a great success in the U.S. and European countries due to their susceptibility to easy copying and illegal distribution. This format did not have the support of the Hollywood entertainment industry for the same reason. These VCDs were also limited in their compatibility with the type of players they could be played back on. Also, the lengthy movies needed to be recorded using two or three VCDs for a single movie. DVD and HD DVD All the previous technologies were able to bring about some progress in home entertainment, but the quality of audio and video achievable were far from the real movie experience. Also, the data storage capacity was far from adequate. This void was filled by the arrival of DVD (Digital Video Disc) in the year 1997. This technology was an instant success as it was capable of providing a much higher quality picture and audio quality than a VHS and could process information much faster than a VCD. The distribution of DVDs at varied intervals in various countries could be achieved using region coding on DVDs and DVD players. The later versions of DVD players were multi region enabled to allow playing of all region DVDs. The DVD players have been designed to playback any TV standard like NTSC, PAL, or SECAM. The recent models of DVD players are compatible with a variety of playing media such as CD-R, CD-RW, DVD-R, DVD-RW, MP3, DivX, and WMA, among others. The HD DVD (High Definition DVD) was formulated in 2003 as a high capacity and enhanced functionality optical disc. Although the DVD and HD DVD are similar in structure, size, and shape, there are many technical differences between the two. The DVD has a data capacity for 4.6GB and can store two hours of 525-line resolution standard definition video. In comparison, the HD DVD has a data storage capacity for 15GB in a single layer disc, which is capable of storing a two hour movie in superior HD format with space for bonus information and also some space to spare. The 30 GB dual layer HD DVD is capable to storing an eight hour, 1,125 lines HD image, or 48 hours of SD image. The proposed triple layer HD DVD would have a 45 GB storage capacity. The DVD is read using a 650nm red laser, whereas the HD DVD is read using a 405nm blue laser. The smaller wavelength allows for data to be read from a higher density of disc surface and creates lesser diffraction. This ability to store data at a higher density gives the HD DVD its higher storage capacity. The optical pick-up head has a numerical aperture of 0.65 in case of HD DVD as compared with the 0.6 of DVD. This similarity allows for backward compatibility for both the technologies. The compression techniques are similar for the two; MPEG-2, Video Codec1 for DVDs and MPEG-4 AVC and VC 1 for HD DVDs. However, the MPEG-2 can only provide a third of the compression possible with MPEG-4. The quality of playback is also more superior with the MPEG-4 compression technique. A unique feature in HD DVDS is its built-in copy restriction or content protection technology, which was developed by AACS LA (Advanced Access Content System License Administrator). It incorporates a Audio Water-mark Protection system that has a waveform altered in such a manner that it acts as a code which is recognizable by a DVD player. This helps the player to differentiate between an original disc and a copy. The copy will be discarded by the player upon detection. None of the previously available media had any such content protection features. The HD DVD players are priced slightly higher than the DVD players, with the Toshiba HD DVD players ranging form $500 to $800. While the Samsung HD DVD players are priced around $140 to $250 varying with the features provided. As the technology becomes widespread and more readily available, the prices will automatically drop with the increase in consumer demand. In a nut shell, the HD DVD discs and players are the most successful audio-visual technology ever to be produced. With its compatibility with the current DVD technology and affordability and unsurpassed quality, it will certainly be the market leader in the home entertainment sector. DVD players and recorders including multi region DVD players and recorders can be purchased at www.planetomni.com in California. They ship worldwide. |
