This means that the video is encoded in the best possible way. The first three parts are Systems, Video and Audio, in that order. Two more parts complete the suite of MPEG-1 standards: Conformance Testing, which specifies the methodology for verifying claims of conformance to the standard by manufacturers of equipment and producers of bitstreams, and Software Simulation, a full C-language implementation of the MPEG-1 standard encoder and decoder.
Manifold have been the implementations of the MPEG-1 standard: from software implementations running on a consumer-grade PC of today in real time, to single boards for PCs, to the so-called Video CD etc. The last product has become a market success in some countries: in China alone millions of Video CD decoders have already been sold. In MPEG-1, video is represented as a sequence of pictures, and each picture is treated as a two-dimensional array of pixels pels.
The color of each pel is consists of three components : Y luminance , Cb and Cr two chrominance components. In order to achieve high compression ratio, MPEG-1 must use hybrid coding techniques to reduce both spatial redundancy and temporal redundancy. These techniques are described as the following :. DCT is used to convert data in time domain to data in frequency domain. If the time domain data is smooth with little variation in data then frequency domain data will make low frequency data larger and high frequency data smaller.
In general, we use large quantization step in quantizing AC coefficients, and use small quantization step to quantize DC coefficient so as to perserve high precision. Below is an example of DCT process :. When encoding I-Picture, we only reduce the spatial redundency in the picture without referencing other pictures. So encodig I-Pcture is less complex than P-frame and B-frame. Decoding I-Picture is inverse process of encoding process, so this section we only describe encoding process.
Before we go further, we must know the basic coding unit is a block which is a 8 by 8 matrix. And a macroblock is consists of six block: 4 block of luminance Y , one block of Cb chrominance, and one block of Cr chrominance. Below is macroblock structure:. I-Picture Encoding Flow Chart. By using this, picture can get good quality but compression ratio is low. So we must use another coding method to code picture like intra-frame coding Will be described in the next section.
This section describes the I-Picture coding process, but not in full details. If you want to implement this encoding process or decoding process you must refer to the MPEG-1 Standard for complete details.
The kind of pictures that are using the intra-frame coding technique are P pictures and B pictures. We will now discuss how these pictures are coded. Coding of the P pictures is more complex than for I pictures, since motion- compensated macroblocks may be constructed. Skip to content. What is Theora format?
Parts 1 Systems , part 2 Video and part 3 Audio of the standard were approved in late The Systems part provide multiplexing and synchronisation support to elementary Audio and Video streams. MPEG-1 video compression is based on the fact that there is a lot of overlap between the different pictures frames. Only the difference between pictures is coded.
A number of tools and mechanisms were defined aiming in particular at good reconstruction quality for video sequences of general nature and more complex content, and to fulfill the requirements of random access: The basic access entity over the sequence is the Group of Pictures GOP. Three picture frame types are defined, which are intraframe-encoded type I as well as the P unidirectional and B bidirectional motion compensated predictive types.
Within a GOP, at least one picture must be an I picture which must be positioned such that the remaining pictures of the GOP can uniquely be decoded. Flexible prediction mode switching forward, backward etc. Accuracy of motion compensation is half pixel. Weighting of DCT coefficients can be applied in quantization for frequency-specific perceptual customization of the quantization fidelity.
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