Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-01-27
2002-07-02
Diep, Nhon (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06414998
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for supplying an image material such as a broadcasting program, and more particularly to the method and the apparatus for inserting an image material such as a commercial film in the main image material such as a broadcasting program.
2. Description of the Related Art
In recent days, the so-called MPEG standard system has been proposed as a technique of compressing and coding a moving picture signal. The MPEG (Moving Picture Image Coding Experts Group) means an organization for studying coding of a moving picture image to be stored. This organization is an abbreviation of a working department of experts for studying standardization of the technique of compressing a moving picture. This organization is established in 1988 under the control of the International Standardization Organization (ISO) and the International Electrotechnical Commission (IEC). The technique of compressing data of a moving picture and speech, standardized by the organization, is referred to as an MPEG system.
The MPEG standards consist of the MPEG1, which is a phase 1 on the standardizing work, and the MPEG2, which is a phase 2 thereon. The difference between them will be briefly described below. The MPEG1 is the standards mainly for storage medium such as a CD-ROM, while the MPEG2 is the standards covering a wide range of medium including an application program of the MPEG1.
The MPEG2 output stream is divided into two types of systems, one of which is referred to as a program stream (MPEG2-PS, PS: Program Stream) and the other of which is referred to as a transport stream (MPEG2-TS TS: Transport Stream). The program stream is intended for the storage medium like the MPEG1. The transport stream is intended for a transmission medium.
This MPEG2 system has a function of transforming plural programs into one stream (data train). Hence, it may correspond to a TV broadcasting program, for example. Further, it allows for free organization of programs and further provides an expansion function and an additional function for various applications. To realize those functions, there are provided directory information for facilitating random access and type information for representing a type of each stream.
The MPEG system has the following flow from coding to decoding.
In the flow of coding in an encoder, a video signal and an audio signal are respectively coded as keeping them associated with each other. Next, each coded stream is multiplexed by a multiplexer in a manner to apply to a format of a transmission medium such as a storage medium or a network of the stream according to the application program. Then, the multiplexed data is transmitted or recorded.
In the flow of decoding in a receiver decoder, on the other hand, the received multiplexed stream is separated into the respective streams such as the video signal stream and the audio signal stream by a demultiplexer and then those separated streams are sent to a decoder. Next, each stream is decoded by a decoder and then is outputted to an output unit (video monitor or a speaker).
As mentioned above, the MPEG system is executed to time-divisionally multiplex plural coded streams into one stream and, on the receiving side, to synchronously decode the multiplexed stream into each stream as intended on the transmission side and reproduce the streams.
The MPEG system has a packet-based multiplexing system as a time-divisional multiplexing system. The packet-based multiplexing is a time-divisional transmitting system for dividing a video signal and an audio signal into streams of a fixed length called a packet, adding additional information such as a header to each packet, and switching the video packet and the audio packet into each other at a proper time in the case of multiplexing the video signal and the audio signal. The packet contains information for identifying an attribute of the signal, which indicates if the signal is a video signal or an audio signal, at the head portion called a header. In some cases, the packet may contain at its tail a CRC (Cyclic Redundancy Code) for detecting a bit error on the transmission.
The packet length strongly depends on the transmission medium and the application. The packet length may be short (53 bytes) as at ATM (Asynchronous Transfer Mode) or long (4096 bytes) like an optical disk system. In the MPEG, the upper length limit of the packet is about 2
16
(64 Kbytes) and the packet length may be fixed or variable for providing the packet with flexibility. Further, the MPEG allows a variable transmission speed so that the intermittent transmission of packets is made possible. The fixedly necessary portions such as the header do not depend on the packet length. Hence, if the packet is short, the overhead (additional data needed for multiplexing) is made so large that the transmission efficiency is dropped. However, the short packet needs only a short switching time for time-divisional multiplexing. Hence, the short packet has a merit that it reduces a delay caused by the multiplexing and a buffer memory in amount.
In the MPEG1 and the MPEG2-PS, the highest layer of the packet of the video signal or the audio signal is called a pack layer. Normally, a pack of bundling plural packets is a constitutional unit when the packets are treated. The pack header contains additional information for referring to a time reference for synchronous reproduction (to be discussed below). The main object of the pack is to provide a capability of decoding and reproducing the stream on its halfway point.
Herein, in the MPEG synchronous system, each decoding and reproducing unit that is referred to as an access unit of the video and the audio signals (the unit of the video signal is one frame and the unit of the audio signal is one audio frame) contains information called a time stamp for indicating when it is to be decoded and reproduced). The time stamp is given a time reference by the information called SCR (System Clock Reference).
The time stamp is a tag for managing a time in the decoding and reproducing process. The tag is added to each access unit. The time stamp is divided into two types of time stamps, one of which is referred to as a PTS (Presentation Time Stamp) and the other one of which is referred to as a DTS (Decoding Time Stamp). The PTS is the information for managing the time of reproduction and output. The DTS is the information for managing the time of decoding. If the head of the access unit is contained in a packet, these time stamps are added to the packet header. If no head of the access unit is contained in the packet, no time stamp is added to the packet header. Further, if two or more heads of the access units are contained in a packet, only the time stamp corresponding to the first access unit is added to the packet header.
As to the PTS, when the STC (System Time Clock) located inside of a reference decoder of the MPEG system coincides with the PTS, the access unit is reproduced and outputted. As to the DTS, the MPEG is arranged so that an I picture and a P picture are placed before a B picture when those pictures are sent out to the coded stream. Hence, the decoding sequence is different from the reproducing and outputting sequence. If the PTS is different from the DTS, both of the time stamps are added. If both coincide with each other, only the PTS is added.
The SCR (System Clock Reference) and the PCR (Program Clock Reference) are the information for setting and calibrating a STC (basic synchronous signal) value, that is, the time standard, into a value intended on the encoder side through the effect of the MPEG system decoder containing a video signal and an audio signal decoders. When using the SCR and the PCR, only the SCR and the PCR are not enough. Further, the timing accuracy (arrival time to the decoder) of the byte in the stream carrying the SCR and the PCR is required. In the MPEG2, the SCR or the PCR is composed of six bytes when they are sent. On the decoder side, on the instance of the a
Suzuki Takao
Yoshinari Hiromi
LandOfFree
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