Comparison Of MPEG-2 And MPEG-4

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Among the MPEG technologies used in practice, the current MPEG-4 offers the highest efficiency during encoding. The main reason is ACE (Advanced Coding Efficiency) - an encoding algorithm that is used in MPEG-4 for the first time.The object orientation in connection with ACE enables very low data rates. It allows storing a complete video movie in full PAL or NTSC resolution and stereo audio (16 bit, 48 kHz) on a single CD-ROM. For clarification: 700 MB of storage is totally sufficient for most movies that run up to 110 minutes. A movie in MPEG-2 format, on the other hand, requires at the same resolution about 11 times more storage space (DVD with 8 GB). While the data rate of MPEG-2 is coupled very closely to the actual profile, MPEG-4 is scalable over a wide area in the audio as well as in the video stream. Audio signals can be processed from 2 kBit/s to 24 kBit/s while video is variable between 5 kBit/s and 10 Mbit/s. Because of this scalability the audio/video data can be adapted specifically to the actual environment. MPEG-2 is mainly used for the large applications: as data format on a video DVD, as data stream in digital television broadcasts and in video editing for digital video broadcasting.

There is an almost unlimited number of applications for the new video format MPEG-4: The home user can store MPEG-2 videos on a CD-ROM. For example it is now possible to convert DVDs into MPEG-4 format at the home PC to play them later on the notebook (without DVD-ROM drive). Audio signals may be broadcasted over the Internet with MPEG-4 compression for "audio on demand". This Digital Audio Broadcasting is possible because it only needs about 16 kBit/s bandwidth. The situation is similar for video services and animations of 2D or 3D objects that can be send over the Internet with different data rates simultaneously. The new mobile radio standard UMTS is also based on MPEG-4 compression technology.

MPEG-4 is the current state-of-the-art for video compression technology. The two older technologies MPEG-1 and MPEG-2 already caused a widespread distribution of digital video on the PC and notebook. The successor of MPEG-4 is already on the horizon and is called MPEG-7. This video standard is supposedly going to be introduced in July 2001 and principally integrates an object search routine. MPEG-2 will also be extended; MPEG-21 is the succeeding standard.

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One thing is certain: With its low data rate combined with comparatively high video quality, MPEG-4 revolutionizes the market for digital video. MPEG-4 offers better compression algorithms than MPEG-1 and MPEG-2. However, encoding of a MPEG-4 sequence requires a lot of computing power: With the Flask Mpeg program even a fast PC takes several hours to convert a movie in MPEG-2 format. But the quality is very respectable: At a selected data rate of 110 kB per second the copy hardly differs from the original.