Pulse or digital communications – Bandwidth reduction or expansion
Reexamination Certificate
1998-03-19
2001-08-21
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Reexamination Certificate
active
06278735
ABSTRACT:
TECHNICAL FIELD
This invention relates, in general, to the field of digital video compression, and in particular, to a rate-control technique suitable for real-time single-pass variable bit rate encoding in a video compression system which employs the MPEG-2 international standard.
BACKGROUND ART
The emergence of various digital video technologies in industries such as broadcast television, communications networks, consumer electronics, and multimedia computers has been increasing at a remarkable rate. This widespread use of applications is motivated by the fact that signal processing, editing and data transfer of digital information is much easier as compared to performing the same tasks with an analog representation. But more importantly, digital video owes its popularity to the several standards that have been created for digital video compression in recent years.
Digital video compression solutions are arguably the most important component of any digital video platform. Since digital video is known to contain an enormous amount of information in uncompressed format, its manipulation, storage, and transmission can become very time consuming and expensive, if not impossible. As a result, digital video compression techniques are needed to reduce the overwhelming volume of the data while preserving the perceptual quality of its content. A compatible video decompression scheme is then used to uncompress the data for playback.
The MPEG-2 international standard formed by the Moving Pictures and Expert Group, and described in ISO/IEC 13818-2, “Information technology—Generic coding of moving pictures and associated audio information: Video, 1996,” which is hereby incorporated herein by reference in its entirety, is intended to satisfy the compression needs of the industries mentioned above. This standard specifies the syntax of the encoded stream and a technique of decoding. It offers great flexibility to the encoder designer allowing the designer to derive his/her own set of compression parameters, and therefore, distinguish his/her product from the rest of the encoders developed by other manufacturers.
The efficiency of the MPEG-2 encoding system is assessed by the fidelity of the perceived video transmitted over a fixed communications bandwidth or stored into a digital medium. For some applications, such as in digital satellite systems, multiple programs are multiplexed into a single large stream for broadcasting, and a bank of MPEG-2 encoders are used to monitor and encode all programs, while maintaining the quality of all received channels. The MPEG-2 stream is sent over either a fixed communications bandwidth or a dynamic bandwidth as in asynchronous transfer mode (ATM) networks. For home consumer video or PC applications, where the size of the storage media is limited, the user would like to accumulate as much information as possible, and an efficient encoder is certainly beneficial in these cases.
Most MPEG-2 encoders are developed to perform in constant bit rate (CBR) mode, where the average rate of the video stream is almost the same from start to finish. A video stream includes a plurality of pictures or frames of various types, such as I, B and P picture types. A picture, depending on its type, may consume more or less bits than the set target rate of the video stream. The CBR rate-control strategy has the responsibility of maintaining a bit ratio between the different picture types of the stream, such that the desired average bit rate is satisfied, and a high quality video sequence is displayed.
Other encoders, including other MPEG-2 encoders, perform in a different mode, defined as a variable bit rate (VBR) mode. Variable bit rate encoding allows each compressed picture to have a different amount of bits based on the complexity of intra and inter-picture characteristics. For example, the encoding of scenes with simple picture content (such as a color test pattern) will consume significantly less bits than scenes with complicated picture content (such as a crowded city street), in order to achieve the same picture quality.
Because of the amount of information that is needed to characterize the video and the complexity of the algorithms needed to interpret the information to effectively enhance the encoding process, VBR encoding is conventionally accomplished in non-real time using two or more passes. In a first pass, encoding is performed and statistics are gathered and analyzed, and in a second pass, the results of the analysis are used to control the encoding process. Although this produces a high quality compressed video stream, it does not allow for real-time operation, nor does it allow for single pass encoding.
Therefore, a need exists for a real-time, single pass variable bit rate encoding scheme that provides high quality videos. A further need exists for a real-time single pass variable bit rate encoding scheme that is easily implementable in hardware.
SUMMARY OF THE INVENTION
The shortcomings of the prior art are overcome and additional advantages are provided through the provision of a method of processing groups of frames. The method includes, for instance, encoding at least one group of frames of an input stream, and determining, prior to encoding the entire input stream, a number of bits to be allocated to another group of frames of the input stream. The another group of frames is to be encoded in a variable bit rate mode. The determining uses one or more parameter of values obtained from the encoding.
In a further embodiment of the invention, the method includes encoding the another group of frames in a single pass variable bit rate mode, wherein the another group of frames is encoded in only one encoding pass.
In yet another embodiment of the invention, the determining includes modulating, for the another group of frames, a slope of a predefined perceptual function, and using the modulated slope in a bit rate equation to determine the number of bits to be allocated.
In a further embodiment, the determining includes determining, for the another group of frames, a translation factor for a predefined perceptual function, and using the translation factor in a bit rate equation to determine the number of bits.
In yet another embodiment of the invention, the determining includes compensating for one or more instability conditions of the input stream, and in a further embodiment, the determining includes using a predefined function to determine the number of bits.
In yet another aspect of the invention, a method of processing groups of frames is provided. The method includes, for example, determining a plurality of parameter values from one or more previously encoded group of frames; computing, for a group of frames to be encoded, in a single pass variable bit rate mode, a slope of a predefined function, in which the computing uses one or more of the plurality of parameter values; and obtaining a bit rate for the group of frames to be encoded, using the computed slope and one or more of the plurality of parameter values.
In another aspect of the present invention, a method of processing groups of frames is provided. The method includes, for instance, determining a number of bits to be allocated to a group of frames of an input stream. The determining uses an instantaneous rate-quantization behavior of the group of frames and a perceptual model indicating a complexity of the group of frames. The method further includes encoding the group of frames using a variable bit rate mode at a rate defined by the determining.
In another aspect of the invention, a single pass variable bit rate encoder is provided. The encoder includes, for example, an encoding engine adapted to encode at least one group of frames of an input stream; and means for determining, prior to encoding the entire input stream, a number of bits to be allocated to another group of frames of the input stream. The another group of frames is to be encoded in a variable bit rate mode. The means for determining uses one or more parameter values obtained from the encoding engine.
In yet another aspect of
Heslin & Rothenberg, P.C.
International Business Machines - Corporation
Kelley Chris
Pivnichny John R.
Vo Tung
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