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Saturday, August 8, 2009

Various popular standards for compressing multimedia data

JPEG stands for Joint Photographic Experts Group. However, what people usually mean when they use the term "JPEG" is the image compression standard they developed. JPEG was developed to compress still images, such as photographs, a single video frame, something scanned into the computer, and so forth. You can run JPEG at any speed that the application requires. For a still picture database, the algorithm doesn't have to be very fast. If you run JPEG fast enough, you can compress motion video -- which means that JPEG would have to run at 50 or 60 fields per second. This is called motion JPEG or M-JPEG. You might want to do this if you were designing a video editing system. Now, M-JPEG running at 60 fields per second is not as efficient as MPEG 2 running at 60 fields per second because MPEG was designed to take advantage of certain aspects of motion video.

Motion JPEG

JPEG compression or decompression that is applied real-time to video. Each field or frame of video is individually processed.


MPEG stands for Moving Picture Experts Group. This is an ISO/IEC (International Standards Organization) body that is developing various compression algorithms. MPEG differs from JPEG in that MPEG takes advantage of the redundancy on a frame-to-frame basis of a motion video sequence, whereas JPEG does not.


MPEG 1 was the first MPEG standard defining the compression format for real-time audio and video. The video resolution is typically 352 x 240 or 352 x 288, although higher resolutions are supported. The maximum bitrate is about 1.5 Mbps. MPEG 1 is used for the Video CD format.


MPEG 2 extends the MPEG 1 standard to cover a wider range of applications. Higher video resolutions are supported to allow for HDTV applications, both progressive and interlaced video are supported. MPEG 2 is used for the DVD - Video and SVCD formats, and also forms the basis for digital SDTV and HDTV.


MPEG 3 was originally targeted for HDTV applications. This was incorporated into MPEG 2, so there is no MPEG 3 standard.


MPEG 4 uses an object-based approach, where scenes are modeled as compositions of objects, both natural and synthetic, with which the user may interact. Visual objects in a scene are described mathematically and given a position in a two- or three-dimensional space. Similarly, audio objects are placed in a sound space. Thus, the video or audio object need only be defined once; the viewer can change his viewing position, and the calculations to update the audio and video are done locally. Classical "rectangular" video, as from a camera, is one of the visual objects defined in the standard. In addition, there is the ability to map images onto computer-generated shapes, and a text-to-speech interface.

MPEG 7 standardizes the description of multimedia material (referred to as metadata), such as still pictures, audio, and video, regardless if locally stored, in a remote database, or broadcast. Examples are finding a scene in a movie, finding a song in a database, or selecting a broadcast channel. The searcher for an image can use a sketch or a general description. Music can be found using a "query by humming" format.

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