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http://whatis.techtarget.com/definition/0,,sid9_gci212603,00.htmlMPEG-1 was designed for coding progressive video at a transmission rate of about 1.5 million bits per second. It was designed specifically for Video-CD and CD-i media. MPEG-1 audio layer-3 (MP3) has also evolved from early MPEG work.
MPEG-2 was designed for coding interlaced images at transmission rates above 4 million bits per second. MPEG-2 is used for digital TV broadcast and DVD. An MPEG-2 player can handle MPEG-1 data as well.
MPEG-1 and -2 define techniques for compressing digital video by factors varying from 25:1 to 50:1. The compression is achieved using five different compression techniques:
- 1. The use of a frequency-based transform called Discrete Cosine Transform (DCT).
2. Quantization, a technique for losing selective information (sometimes known as lossy compression) that can be acceptably lost from visual information.
3. Huffman coding, a technique of lossless compression that uses code tables based on statistics about the encoded data.
4. Motion compensated predictive coding, in which the differences in what has changed between an image and its preceding image are calculated and only the differences are encoded.
5. Bi-directional prediction, in which some images are predicted from the pictures immediately preceding and following the image.
The first three techniques are also used in JPEG file compression.
A proposed
MPEG-3 standard, intended for High Definition TV (HDTV), was merged with the MPEG-2 standard when it became apparent that the MPEG-2 standard met the HDTV requirements.
MpeG-4 is a much more ambitious standard and addresses speech and video synthesis, fractal geometry, computer visualization, and an artificial intelligence (AI) approach to reconstructing images. MPEG-4 addresses a standard way for authors to create and define the media objects in a multimedia presentation, how these can be synchronized and related to each other in transmission, and how users are to be able to interact with the media objects.
MPEG-21 provides a larger, architectural framework for the creation and delivery of multimedia. It defines seven key elements:
- Digital item declaration
- Digital item identification and declaration
- Content handling and usage
- Intellectual property management and protection
- Terminals and networks
- Content representation <li>Event reporting
</li>
The details of various parts of the MPEG-21 framework are in various draft stages.
MP3 is dus wat anders, dat is MPeg-1 Layer 3 ofzo
http://whatis.techtarget.com/definition/0,,sid9_gci212600,00.html<h1>MP3</h1>
MP3 (MPEG-1 Audio Layer-3) is a standard technology and format for compression a sound sequence into a very small file (about one-twelfth the size of the original file) while preserving the original level of sound quality when it is played. MP3 files (identified with the file name suffix of ".mp3") are available for downloading from a number of Web site. Many Windows 98 users will find that they have a player built into their operating system. Otherwise, you can download a player from one of several popular MP3 sites. MP3 files are usually download-and-play files rather than streaming sound files that you link-and-listen-to with RealPlayer and similar products (However, streaming MP3 is possible.) Winamp (PC), MacAmp (Mac), and mpeg123 (UNIX) are popular MP3 players, but there are many others. To create an MP3 file, you use a program called a ripper to get a selection from a CD onto your hard disk and another program called an encoder to convert the selection to an MP3 file. Most people, however, simply download MP3s from someone else and play them.
digital audio is typically created by taking 16 binary digit samples a second of the analog signal. Since this signal is typically spread out over a spectrum of 44.1 thousand cycles per second (kHz), this means that one second of CD quality sound requires 1.4 million bits of data. Using their knowledge of how people actually perceive sound, the developers of MP3 devised a compression algorithm that reduces data about sound that most listeners can not perceive. MP3 is currently the most powerful algorithm in a series of audio encoding standards developed under the sponsorship of the Motion Picture Experts Group (MPEG) and formalized by the International Organization for Standardization (ISO).
Since it is relatively easy to create MP3 files from CD selections and make them available on Web sites for downloading, companies and sites that promote the MP3 format are sometimes accused of encouraging copyright violations. (It is illegal to copy music from a CD and redistribute it unless you have the copyright owner's permission.) On the other hand, MP3 enthusiasts claim that what CD publishers are afraid of is any kind of non-CD distribution. While there are several proposals for how to discourage such piracy, there is currently no secure distribution and copyright management standard that publishers and other parties agree upon.
Several Web sites are promoting MP3 as both a high-quality audio format and as a way in which self-publishers can gain ready access to an audience. Currently, some music publishers are providing sample cuts in the MP3 format as a way to entice users to buy a CD. However, not much mainstream copyrighted material is available except as an illegal download.
As an alternative approach to individual MP3 downloads, IBM and five recording companies plan to offer entire CD downloads to users with access to high-bandwidth cable modem service. Formerly called Madison, the service, which will be tested during 1999, will ensure royalty payment to the artists and publishers. The Recording Industry Association of America (RIAA) is also working on a Secure Digital Music Initiative (SDMI).
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