Digital Versatile Disk (aka digital video disk) – invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995 as a high-density development of the compact disk. It is the same size as a CD, 12 cm diameter, but stores upwards of 4.38 GB of actual data (seven times CD capacity) on a single-sided, single-layer disk. DVDs can also be double-sided or dual-layer – storing even more data.
The capacities commonly available are:
DVD-5 Single-side, single-layer 4.7 GB
DVD-9 Single-side, dual-layer 8.5 – 8.7 GB
DVD-10 Double-sided, single-layer 9.4 GB
DVD-18 Double-sided, dual-layer 17.08 GB
DVD-5 and DVD-9 are widely used. However the double-sided disks are quite rare, partly because they are more difficult to make and they cannot carry a label.
There are various types of DVD including:
DVD-R – recordable DVDs with a data capacity of 4.38 GB are popular and low priced.
DVD+R – dual layer recordable DVDs with a total capacity of two DVD-Rs.
DVD-RAM – re-recordable DVD, re-use up to around 100,000 times. Capacity of 4.38 GB (single-sided). Some camcorders have use these – they offer instant access to shot material and record loop features – useful when waiting to record an event, like a goal, to happen. At home it can provide a removable media alternative. A particular feature is that it can record and replay at the same time.
DVD-Video – combines the DVD with MPEG-2 video compression, with multichannel audio, subtitles and copy protection capability.
To maximize quality and playing time DVD-Video uses variable bit rate (VBR) MPEG-2 coding where the bit rate varies with the demands of the material. Typically a 525/60 TV format, 24 f/s movie would use an average bit rate of 3.5 Mb/s, but for sections with a great deal of movement it could peak at 8 or 9 Mb/s. Only 24 f/s are coded onto the disk, the 3:2 pull-down conversion to 30 f/s taking place in the player. This allows a 120-minute 24 f/s movie to fit on a DVD-5. To store video (not film) with 50 or 60 discrete fields per second, the bit rate tends to average around 6 or 7 Mb/s, but again depends on the running time, original material and desired picture quality.
CBHD China Blue High-Definition or China High Definition DVD is a variant of HD DVD which is only used within China.
Multi-channel audio DVD-Video supports PCM, MPEG and Dolby Digital audio, for anything from mono, stereo, Dolby Surround to 5.1 channels. Digital Theatre Sound (DTS) and Sony Dynamic Digital Sound (SDDS) are options. Up to eight separate audio streams can be supported, allowing multiple languages, audio description, director’s commentary, etc. For example, a release may have 5.1 Dolby Digital English, two-channel Dolby Digital Spanish with Dolby Surround, and mono French.
Region coding Disks can be region-coded and so only play in a particular region (as defined in the player), a set of regions or be ‘code-free’.
The region numbers are:
- Canada, US, US Territories
- Japan, Europe, South Africa, Middle East (including Egypt)
- Southeast Asia, East Asia (including Hong Kong)
- Australia, New Zealand, Pacific Islands, Central America, South America, Caribbean
- Former Soviet Union, Indian Subcontinent, Africa (also North Korea, Mongolia)