Television – Bandwidth reduction system – Format type
Patent
1996-05-23
1998-06-16
Burgess, Glenton B.
Television
Bandwidth reduction system
Format type
348429, 348384, 375240, H04N 712, H04N 704
Patent
active
057679126
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention is related to the field of digital signal processing, and more particularly to method and apparatus for assembling transport data packets such as may be used for conveying coded MPEG-like data in a high definition television system, for example.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,168,356--Acampora et al. describes a system for processing a high definition television (HDTV) signal subjected to MPEG-like variable length coding. MPEG is a standardized coding format being established by the International Organization for Standardization. The standard is described in the document "International Organization for Standardization," ISO/IEC DIS 11172, Coding for Moving Pictures and Associated Audio for Digital Storage Media, Rev. Nov. 23, 1991 which document is incorporated herein by reference for description of the general code format. In the Acampora et al. system, codewords are prioritized to reflect high priority and low priority information in a datastream. The codeword datastream is passed to a transport processor which packs the codeword data into transport cells each including header and packed data payload sections, and which provides output high priority and low priority datastreams.
A major function of the transport processor is to pack variable length codeword data, issued by a preceding priority processor, into packed data words. An accumulation of packed words, called a data packet, is prefaced with a transport header.
The transport packet format enhances resynchronization and signal recovery at a receiver, e.g., after a signal disruption due to a transmission channel disturbance, by providing header data from which a receiver can determine re-entry points into the data stream on the occurrence of a loss or corruption of transmitted data. Synchronization of data at an MPEG decoder also is facilitated by a Group of Pictures (GOP) beginning at a packet boundary. As will be seen, a GOP is a series of one or more pictures, or frames, intended to assist random access into a coded video bitstream sequence. Resynchronization is also facilitated by responding to an intracoded I-frame picture start codeword, and by placing the picture start codeword at a packet boundary, e.g., in a system according to the MPEG standard. Apparatus in accordance with the principles of the present invention facilitates the development of a transport packet.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, a special indicator is inserted into an image representative codeword datastream comprising a succession of blocks of grouped pictures. The indicator occurs prior to a group of pictures to indicate the imminent appearance thereof.
In a disclosed preferred embodiment, a special codeword, a Packet Alignment Flag (PAF), is inserted into an MPEG datastream to signify the beginning of a Group of Pictures (GOP). The PAF immediately precedes a Picture Start codeword for an intracoded "I" frame, which initiates a GOP. The PAF indicates the imminent appearance of a Picture Start codeword, and encompasses one clock cycle during which certain "housekeeping" functions are performed before the Picture Start codeword appears at the beginning of the next packet. These housekeeping functions include, for example, resetting accumulators, checking header data, and generating a Last Word Indicator for the data packet under construction when the PAF appeared. When the PAF appears, a data packet under construction is terminated, since a GOP is intended to begin at a packet boundary. Such termination may result in an abbreviated packet containing less than a prescribed number of packed words.
According to an aspect of the invention, the last word of each packet is designated as such to facilitate the subsequent formation of a transport packet.
In accordance with another aspect of the invention, an abbreviated data packet is filled with null (zeroed bits) words to make up a complete data packet with a prescribed number of words, and to define an inter-packet boun
REFERENCES:
patent: 5121205 (1992-06-01), Ng et al.
patent: 5122875 (1992-06-01), Raychaudhuri et al.
patent: 5168356 (1992-12-01), Acampora et al.
patent: 5241382 (1993-08-01), Paik et al.
patent: 5289276 (1994-02-01), Siracusa et al.
patent: 5440345 (1995-08-01), Shimoda
patent: 5598415 (1997-01-01), Nuber et al.
Acampora Alfonse Anthony
Brooks Charles Alan
Bunting Richard Michael
Harris David Isaac
Burgess Glenton B.
General Electric Company
Herrmann Eric P.
Kurdyla Ronald H.
Tripoli Joseph S.
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