Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2001-08-13
2004-11-23
An, Shawn S. (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240150, C375S240160, C375S240260, C348S705000, C348S512000, C370S487000, C370S490000, C370S498000, C382S232000, C382S238000
Reexamination Certificate
active
06823010
ABSTRACT:
The present invention relates to a method switching the video component(s) of a first digital, audio-visual program onto the video component(s) of a second digital, audio-visual program.
The invention applies to the field of digital, audio-visual services wherein digital programs consist of at least one video component and may comprise several video components, none or several audio components, and none or several data components. The invention relates only to the video components.
Pertinent digital audio-visual services include those using the so-called MPEG-2 standard (Moving Pictures Expert Group) ISO/IEC JTC1 IS 13818. This standard is described in several documents each corresponding to a distinct portion (video, audio, system, conformity etc.)
Nevertheless it is to be understood that the present invention is not restricted to solely following this particular MPEG-2 standard but also covers any digital, audio-visual service application.
Three kinds of pictures are defined generally, and in particular in the video portion of the MPEG-2 standard:
The so-called I images (Intra-coded pictures] that do not refer to any other picture; these are moderate compression-ratio pictures; their coding does not imply using methods of motion estimates,
The so-called P pictures (predictive code pictures) which are coded by using prediction methods estimating motion that are based on a preceding picture which may be a type I picture or a type P picture,
The so-called B pictures (bidirectionally predictive-coded pictures) which are coded using motion prediction methods based on a preceding picture (called back prediction for displays) which then are I or P type.
In general the video components discussed in the present invention therefore consist of an ordered string of Intra, predictive- or bidirectional pictures of which the order varies depending on involving the order of presentation or the order of transmission.
One illustrative application of a method of the present invention concerns chaining different TV programs. It involves switching from a first program selected from a given number of a first multiplex' programs to a second program selected from a given number of a second multiplex' programs and possibly, later, in switching again from the second program to the first.
In other words, a first program is disconnected in order to connect to second program, and back. These operations entail two multiplexes of the same syntax which are coded in real time or are retrieved from a storage system.
This application incurs a difficulty which shall now be described in relation to
FIGS. 1 and 2
and within the narrower scope of a system adhering to the MPEG-2 standard. Before that, however, said standard will be elucidated.
The audio and video portions of the MPEG-2 standard describe how to digitally code the video and audio data. According to the system part of the MPEG-2 standard, the resultant compressed elementary streams are transformed into elementary stream packets PES (Packetized Elementary Streams). The PES packets containing video data may be of constant or variable sizes. The illustrative embodiment described below relates to using PES video packets of variable size, each PES packet comprising a single picture (possibly with sequence headers or picture groups GOP headers), the pictures being aligned at the beginning of the PES packet. The PES packets moving in the same elementary stream are identified by the same identifier called Stream ID.
The system standard MPEG-2 also specifies that the PES packets (video, audio or data) may be multiplexed for local use for instance with PES signaling packets. Such a multiplex may be stored on disk such as those known as DVD (Digital Versatile Disk), for instance it relates to the program of MPEG-2 syntax.
According to the system MPEG-2 standard, the elementary stream formed into PES packets may then be segmented into fixed-size packets called transport packets (TP). Such a fixed-size packet is identified by a packet identifier (PID). A stream of PES packets having the same Stream ID can only move in transport packets with the same packet identifier PID. The transport packets moving a particular elementary stream (and the PES packets having for the first time segmented this elementary stream) may be multiplexed with other TP transport packets moving other elementary streams, not excluding however TP transport packets containing signaling information etc. The TP transport multiplexes then will be suitable for transmission and their organization then will be determined by the transport MPEG-2 syntax.
The video MPEG-2 standard calls provides six hierarchical levels for the syntax of a video elementary stream: the sequence, the so-called group of pictures (GOP) which is the only optional level, the picture (type I, P or B), the image slice, the macro block and the block.
A video sequence begins with a sequence header which is followed by one or more sets of pictures. According to MPEG-2, these sets of pictures may be combined into groups of pictures GOP. One group of pictures GOP is characterized by a header of a group of pictures GOP situated ahead of the pictures. In the order of transmission, the group of pictures GOP begins with an I picture followed by a given number of bidirectional pictures B and predictive pictures P, and this in a rigorous order. A group of pictures GOP is said to be open when its first pictures B refer to the last picture P of the preceding set or to the group of pictures GOP; it is called closed when there is no such reference. The invention is appropriate for the video elementary streams codes as an open group of pictures GOP.
In general the program video components consists of strings of sequences with one group of pictures GOP per sequence. In a stretch of terminology, any group of pictures GOP shall be called hereafter such a group which is preceded by a sequence header.
Each picture comprises a header and data consisting of a number of slices. A slice pools several continuous macro-blocks in the picture. In conventional digital television (format 4; 2; 0), one micro-block is the combination of four luminance blocks, one block of a first chrominance component for the same pixels and one block of a second chrominance component also for the same pixels. Illustratively one block contains the data of eight by eight pixel squares.
The illustrative implementation of the invention described below is situated at the level of the MPEG-2 transport portion, however the operations carried out at the elementary level and at the level of the PES packets are directly applicable to the MPEG-2 program standard.
Even if all precautions have been taken to terminate the first video component at the sequence end (and at the end of group of pictures GOP) and to start the second video component at the beginning of the sequence (and hence at the beginning of the group of images GOP), there is a major problem when switching a first digital, audio-visual program of conventional television onto a second one, namely the degradation of the resultant picture. It is known that this degradation takes place when the coding of the first pictures B refers to the last picture P or I of the preceding sequence. If the concept of group of pictures GOP is used, this coding is called “coding in open group of images GOP”: the appearance of a mosaic in the restored picture is caused by the rupture of the rear reference of the first bidirectional pictures B of each new group of pictures.
Be it borne in mind that each program may comprise several video components, for instance components which are of different views in the program (for instance from several cameras). The invention does apply to each of these components; however, for the sake of clarity, only one video component shall be discussed for each program.
Be it also noted that
FIG. 1
is free of the PES packet and transport packet levels. This
FIG. 1
represents an elementary video stream F
1
of a first program and an elementary video stream F
2
of a second program. Each stream F
1
Curet Dominique
Douteau Andre
Garault Therese
Hellegouarch Gerard
Lolivier Germain
An Shawn S.
France Telecom (SA)
Lowe Hauptman & Gilman & Berner LLP
LandOfFree
Method for switching a first digital audio-visual program... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for switching a first digital audio-visual program..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for switching a first digital audio-visual program... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3321657