CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [210]
With the exception of the DVD logo stamped on all commercial DVDs (see Figure 13-25), DVDs look exactly like CD-media discs; but that’s pretty much where the similarities end. DVD has become the fastest growing media format in history and has completely overtaken VHS as the preferred media for video. Additionally, one variant of DVD called DVD-RAM has enjoyed some success as a mass storage medium.
The single best word to describe DVD is capacity. All previous optical discs stored a maximum of 700 MB of data or 80 minutes of video. The lowest capacity DVD holds 4.37 GB of data, or two hours of standard-definition video. The highest capacity version DVDs store roughly 16 GB of data, or more than eight hours of video! DVD achieves these amazing capacities by using a number of technologies, but three are most important. First, DVD uses smaller pits than CD-media, and packs them much more densely. Second, DVD comes in both single-sided (SS) and double-sided (DS) formats. As the name implies, a DS disc holds twice the data of an SS disc, but it also requires you to flip the disc to read the other side. Third, DVDs come in single-layer (SL) and dual-layer (DL) formats. DL formats use two pitted layers on each side, each with a slightly different reflectivity index. Table 13-1 shows the common DVD capacities.
Figure 13-25 Typical DVD-video
Table 13-1 DVD Versions/Capacities
DVD-Video
The most beautiful trait of DVD-video lies in its capability to store two hours of video on one side. You drop in a DVD-video and get to watch an entire movie without flipping it over. DVD-video supports TV-style 4:3 aspect-ratio screens as well as 16:9 theater screens, but it is up to the producer to decide which to use. Many DVD-video producers distribute DVD movies on DS media with a 4:3 ratio on one side and 16:9 ratio on the other. DVD-video relies on the MPEG-2 standard of video and audio compression to reach the magic of two hours of video per side. Moving Picture Experts Group (MPEG) is a group of compression standards for both audio and video. The MPEG-2 standard offers resolutions of up to 1280 × 720 at 60 frames per second (fps), with full CD-quality audio (standard DVDs only offer 480 vertical resolution, the same as regular television). Let’s detour into MPEG standards for a moment and then dive back into DVDs.
MPEG Standards Reproducing video and sound on the PC provides interesting challenges for developers. How do you take a motion picture from film, translate it into ones and zeroes that the CPU understands, process those bits, and then send high-quality video and sound to the monitor and speakers for the pleasure of the computer user? How much data do you think is required to display even a two-minute clip of a car racing through a city street, in all the minute detail of the shops, people, screeching tires, road debris, and so on? For that matter, how do you store the obviously huge amount of data required to do this?
To handle these chores, the MPEG has released coding standards such as MPEG-1, MPEG-2, and MPEG-4. Each standard provides a different compression algorithm, which makes the files manageable. The standards also implement various technologies to handle movement, called motion compensation. The details of the standards matter a lot to the folks producing the movies and other video and audio content, but here’s the short answer that should suffice for the purposes of a PC tech.
MPEG-1 is the standard on which video and MP3, among other technologies, are based. The most common implementations of this standard provide a resolution of 352 × 240 at 30 fps. This video quality falls just below that of a conventional VHS video.
One very well-known subset of MPEG-1 is better known for audio than video.