DVD-Video
DVD-Video is a consumer video format used to store digital video on DVDs. DVD-Video was the dominant consumer home video format in Asia, North America,[5] Europe, and Australia in the 2000s until it was supplanted by the high-definition Blu-ray Disc. Discs using the DVD-Video specification require a DVD drive and an MPEG-2 decoder (e.g., a DVD player, or a computer DVD drive with a software DVD player). Commercial DVD movies are encoded using a combination of MPEG-2 compressed video and audio of varying formats (often multi-channel formats as described below). Typically, the data rate for DVD movies ranges from 3 to 9.5 Mbit/s, and the bit rate is usually adaptive. DVD-Video was first available in Japan on November 1, 1996 (with major releases beginning December 20, 1996),[4] followed by a release on March 26, 1997 in the United States—to line up with the 69th Academy Awards that same day.[6]
The DVD-Video specification was created by DVD Forum and can be obtained from DVD Format/Logo Licensing Corporation for a fee of $5,000.[7][8] The specification is not publicly available and every subscriber must sign a non-disclosure agreement. Certain information in the DVD Book is proprietary and confidential.[7]
To record digital video, DVD-Video uses either H.262/MPEG-2 Part 2 compression at up to 9.8 Mbit/s (9,800 kbit/s) or MPEG-1 Part 2 compression at up to 1.856 Mbit/s (1,856 kbit/s). DVD-Video supports video with a bit depth of 8 bits per color, encoded as YCbCr with 4:2:0 chroma subsampling.[9][10]
The following formats are allowed for H.262/MPEG-2 Part 2 video:[11]
The following formats are allowed for MPEG-1 video:
The MPEG-1 Part 2 format does not support interlaced video. The H.262/MPEG-2 Part 2 format supports both interlaced and progressive-scan content, and can handle different frame rates from the ones mentioned above by using pulldown. This is most commonly used to encode 23.976 frame/s content for playback at 29.97 frame/s. Pulldown can be implemented directly while the disc is mastered, by actually encoding the data on the disc at 29.97 frames/s; however, this practice is uncommon for most commercial film releases, which provide content optimized for display on progressive-scan television sets.
Alternatively, the content can be encoded on the disc itself at one of several alternative frame rates, and use flags that identify scanning type, field order and field repeating pattern. Such flags can be added in video stream by the H.262/MPEG-2 Part 2 encoder.[12][13] A DVD player uses these flags to convert progressive content into interlaced video in real time during playback, producing a signal suitable for interlaced TV sets. These flags also allow reproducing progressive content at their original, non-interlaced format when used with compatible DVD players and progressive-scan television sets.[14][15]
The audio data on a DVD movie can be Dolby Digital (AC-3), DTS, PCM, or MPEG-1 Audio Layer II (MP2) format. In countries using the PAL system standard DVD-Video releases must contain at least one audio track using the PCM, MP2, or AC-3 format, and all standard PAL players must support all three of these formats. A similar standard exists in countries using the NTSC system, though with no requirement mandating the use of or support for the MP2 format. DTS audio is optional for all players, as DTS was not part of the initial draft standard and was added later; thus, many early players are unable to play DTS audio tracks. Only PCM and DTS support 96 kHz sampling rate. Because PCM, being uncompressed, requires a lot of bandwidth and DTS is not universally supported by players, AC-3 is the most common digital audio format for DVDs, and 96 kHz is rare on a DVD. The official allowed formats for the audio tracks on a DVD-Video are:
DVDs can contain more than one channel of audio to go together with the video content, supporting a maximum of eight simultaneous audio tracks per video. This is most commonly used for different audio formats—DTS 5.1, AC-3 2.0 etc.—as well as for commentary and audio tracks in different languages.
Data rate[edit]
DVD-Video discs have a raw bitrate of 11.08 Mbit/s, with a 1.0 Mbit/s overhead, leaving a payload bitrate of 10.08 Mbit/s. Of this, up to 3.36 Mbit/s can be used for subtitles, a maximum of 10.08 Mbit/s can be split amongst audio and video, and a maximum of 9.80 Mbit/s can be used for video alone.[17] In the case of multiple angles the data is stored interleaved, and so there is a bitrate penalty leading to a max bitrate of 8 Mbit/s per angle to compensate for additional seek time. This limit is not cumulative, so each additional angle can still have up to 8 Mbit/s of bitrate available.
Professionally encoded videos average a bitrate of 4–5 Mbit/s with a maximum of 7–8 Mbit/s in high-action scenes. Encoding at less than the max bitrate (like this) is typically done to allow greater compatibility among players,[18] and to help prevent buffer underruns in the case of dirty or scratched discs.
In October 2001, aiming to improve picture quality over standard editions, Columbia TriStar Home Entertainment offered "Superbit"—a premium line of DVD-Video titles having average bitrates closer to 6 Mbit/s. Audio quality was also improved by the mandatory inclusion of both Dolby Digital and DTS 5.1 surround audio tracks. Multiple languages, angles, and extra audio tracks were eliminated to free up more space for the main title and thereby to ensure the highest data rate possible. In January 2007 the Superbit line was discontinued.
Programming interface[edit]
A virtual machine implemented by the DVD player runs bytecode contained on the DVD. This is used to control playback and display special effects on the menus. The instruction set is called the Virtual Machine (VM) DVD command set. There are 16 general parameter registers (GPRM) to hold temporary values and 24 system parameters (SPRM). As a result of a moderately flexible programming interface, DVD players can be used to play games, such as the DVD re-release of Dragon's Lair, along with more sophisticated and advanced games such as Scene It?, all of which can be run on standard DVD players.