Post by juju on Apr 4, 2006 4:16:55 GMT -5
Moving Picture Experts Group (MPEG)
MPEG is the standards committee, supported by the ISO (International Standards Organization) that developed the MPEG standards for digital video (sequences of images in time) and audio compression. The committee was established to create uniform methodologies and algorithms for these files.
The core technology of MPEG incorporates many different patents from many different companies and individuals worldwide. But the MPEG committee is not involved with the patents and intellectual property issues of these companies. It only establishes the technical standards, which began with Resolution 3.9.6, adopted in New York in July 1993 as an effort to form an MPEG related licensing entity that would provide efficient access to IPR (intellectual property rights) necessary for the implementation of MPEG technology worldwide.
But MPEG is also the type (and file extension) of the actual compressed audio and video files. With MPEG, the size of an audio or video file is significantly reduced without compromising audio/video quality. For example, an uncompressed three-minute song uses about 30MB of drive space. With MP3 compression, that same 30MB audio file is reduced to approximately 3MB without any noticeable difference in sound quality.
Essentially, these compression rates provide radio broadcasting over the Internet with CD quality music, which has become a major promotional vehicle for bands and musical artists on the Web. With a 28.8Kbps (kilobits per second) modem, MP3 songs can be transmitted or downloaded from the Internet in about 10 minutes or less, as opposed to two hours or more without this compression technique.
Currently, MPEG has four levels of audio/video compression:
• MPEG-1, developed in 1992, supports video and audio data storage and retrieval at about 1.5Mbps (megabits per second). The video is defined for noninterlaced, computer type data streams, and usually, MPEG-1 video compression ranges up to 100:1 for images with 352 pixels x 288 lines at a refresh rate of 30fps (frames per second).
• MPEG-2, completed in November 1994, also supports video and audio data storage and retrieval but at bit rates up to 10Mbps. MPEG-2 video compression, however, is defined for interlaced broadcast television, which is a more advanced standard, and provides higher resolution and additional features, such as scalability and the ability to place pictures within pictures.
• MPEG-3, which targeted HDTV (high-definition television) applications, had sampling dimensions up to 1,920 x 1,080 x 30Hz (hertz) and coded bit rates between 20Mbps and 40Mbps. MPEG-3, however, did not last. The MPEG committee discovered that with some fine-tuning, the MPEG-2 and MPEG-1 syntax worked just as well for HDTV rate video.
• MPEG-4 is a proposed standard for video compression with bit rates at tens of kilobytes and below. This standard is targeted to manage applications for digitally encoded moving pictures and synchronized audio that can only handle very low bit rates—for example, public switched telephone networks and low-cost wired and wireless networks.
For video, however, MPEG can compress data as many as 200 times, based on the original video’s quality and the preferred quality of output. This can be accomplished because the MPEG standard uses the JPEG (Joint Photographic Experts Group) algorithm for compressing individual frames and eliminates the redundant data in successive frames (just like JPEG graphic files). For example, if the background is exactly the same in 300 frames of a 500-frame video clip, MPEG only copies the background information of one frame instead of 300 frames. It eliminates the redundant data and thus reduces the file’s size.
MPEG is the standards committee, supported by the ISO (International Standards Organization) that developed the MPEG standards for digital video (sequences of images in time) and audio compression. The committee was established to create uniform methodologies and algorithms for these files.
The core technology of MPEG incorporates many different patents from many different companies and individuals worldwide. But the MPEG committee is not involved with the patents and intellectual property issues of these companies. It only establishes the technical standards, which began with Resolution 3.9.6, adopted in New York in July 1993 as an effort to form an MPEG related licensing entity that would provide efficient access to IPR (intellectual property rights) necessary for the implementation of MPEG technology worldwide.
But MPEG is also the type (and file extension) of the actual compressed audio and video files. With MPEG, the size of an audio or video file is significantly reduced without compromising audio/video quality. For example, an uncompressed three-minute song uses about 30MB of drive space. With MP3 compression, that same 30MB audio file is reduced to approximately 3MB without any noticeable difference in sound quality.
Essentially, these compression rates provide radio broadcasting over the Internet with CD quality music, which has become a major promotional vehicle for bands and musical artists on the Web. With a 28.8Kbps (kilobits per second) modem, MP3 songs can be transmitted or downloaded from the Internet in about 10 minutes or less, as opposed to two hours or more without this compression technique.
Currently, MPEG has four levels of audio/video compression:
• MPEG-1, developed in 1992, supports video and audio data storage and retrieval at about 1.5Mbps (megabits per second). The video is defined for noninterlaced, computer type data streams, and usually, MPEG-1 video compression ranges up to 100:1 for images with 352 pixels x 288 lines at a refresh rate of 30fps (frames per second).
• MPEG-2, completed in November 1994, also supports video and audio data storage and retrieval but at bit rates up to 10Mbps. MPEG-2 video compression, however, is defined for interlaced broadcast television, which is a more advanced standard, and provides higher resolution and additional features, such as scalability and the ability to place pictures within pictures.
• MPEG-3, which targeted HDTV (high-definition television) applications, had sampling dimensions up to 1,920 x 1,080 x 30Hz (hertz) and coded bit rates between 20Mbps and 40Mbps. MPEG-3, however, did not last. The MPEG committee discovered that with some fine-tuning, the MPEG-2 and MPEG-1 syntax worked just as well for HDTV rate video.
• MPEG-4 is a proposed standard for video compression with bit rates at tens of kilobytes and below. This standard is targeted to manage applications for digitally encoded moving pictures and synchronized audio that can only handle very low bit rates—for example, public switched telephone networks and low-cost wired and wireless networks.
For video, however, MPEG can compress data as many as 200 times, based on the original video’s quality and the preferred quality of output. This can be accomplished because the MPEG standard uses the JPEG (Joint Photographic Experts Group) algorithm for compressing individual frames and eliminates the redundant data in successive frames (just like JPEG graphic files). For example, if the background is exactly the same in 300 frames of a 500-frame video clip, MPEG only copies the background information of one frame instead of 300 frames. It eliminates the redundant data and thus reduces the file’s size.