MPEG-1 is the name of a group of audio encoding standards and standardized by the (Moving Picture Experts Group) MPEG video group. MPEG-1 video is used for Video CD format. The output quality with usual compression rate used in VCD is similar to a VHS home video cassette. For audio, the MPEG group defined the MPEG-1 audio layer 3 known as MP3.
MPEG-1 Part 3 Layer 1
Operates at bit rates in the range of 32-448 kb/s support and sampling frequencies of 32, 44.1 and 48 kHz.
MPEG-1 Part 3 Layer 2
Layer 2 is designed for applications requiring low complexity decoding and encoding. Layer 2 provides an efficiency higher compression with a slightly greater complexity. The MPEG-1 Layer one can compress data CD audio quality at a rate of 384 bits typical kb/s, while maintaining high audio quality after decoded.
MPEG-1 Part 3 Layer 3
The perceptual audio coder of the standard, provides excellent compression of music signals. Compared to layer 1 and layer 2 provides a higher compression efficiency. Usually you can compress the data of an audio CD of high quality with a factor of 12, while maintaining high audio quality. Overall MP3 is suitable for applications involving the storage or transmission mono or stereo music or other audio signals. Since its implementation, it is used in virtually all digital playback devices audio.
Thanks to its low complexity decoding combined with high robustness encoding/decoding cascade and transmission errors, MPEG-1 Layer 2 is used in video transmission applications (DVB and DAB) and digital audio. It is also used in video CD and in a variety of applications study.
Layer 3, or as it is called today “mp3”, is the most widespread audio encoding format for storing music on PC platforms, and streaming music over the Internet. Mp3 has created a new class of consumer electronics devices that bears his name, the mp3 player. It is found in almost all CD and DVD and an increasing number of new car and home stereo devices, for example music servers networked home. In addition, layer 3 has a wide application in digital audio broadcasting satellite and mobile phones. MPEG-1 Layer 3 is normalized for sample rates higher than 32, 44.1 and 48 kHz.
MPEG-4 provided lower bit rates (10Kb/s to 1Mb/s) with a good quality. It was a major development from MPEG-2 and was designed for the use in interactive environments, such as multimedia applications and video communication. It enhances the MPEG family with tools to lower the bit-rate individually for certain applications. It is therefore more adaptive to the specific area of the video usage. For multimedia producers, MPEG-4 offers a better reusability of the contents as well as a copyright protection. The content of a frame can be grouped into object, which can be accessed individually via the MPEG-4 Syntactic Description Language (MSDL). Most of the tools require immense computational power (for encoding and decoding), which makes them impractical for most “normal, nonprofessional user” applications or real time applications. [Mitrovich]
The MPEG Compression
The MPEG compression algorithm encodes the data in 5 steps, First a reduction of the resolution is done, which is followed by a motion compensation in order to reduce temporal redundancy. The next steps are the Discrete Cosine Transformation (DCT) and a quantization as it is used for the JPEG compression; this reduces the spatial redundancy (referring to human visual perception). The final step is an entropy coding using the Run Length Encoding and the Huffman coding algorithm. [Mitrovich]
- Step 1: Reduction of the Resolution.
- Step 2: Motion Estimation.
- Step 3: Discrete Cosine Transform (DCT).
- Step 4: Quantization.
- Step 5: Entropy Coding.
Extensions Associated with MPEG Standard