Device for splitting a screen in MPEG image signals at a completely compressed domain and the method thereof

The invention provides a method of multiplexing moving pictures fed from a plurality of multimedia communication terminals through broadband Integrated Service Distance Network (B-ISDN) and displaying a multiplexed moving picture on a display unit of the plurality of terminals, which comprising the steps of checking a type and a performance of the terminals, and assistance possible performance of the MCU to the terminals by end-and-end signaling; and selecting M terminals among the plurality of terminals connected thereto; generating a start signal to the selected M terminals, the start signal allowing each of the selected terminals to generate the moving picture to be processed; processing a first and second moving pictures generated from two terminals in response to the start signal; processing a third and four moving pictures generated from two terminals in response to the start signal; repeating said steps until all of moving pictures from the selected M terminals are inputted.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to digital video signal processing; and more 
particularly, to a device for splitting a screen expressed in moving 
picture signals compressed by MPEG (Moving Picture Expert Group) on a 
completely compressed domain by employing an non-transcoding technique, in 
image processing functions of a Multipoint Control Unit (MCU) which is 
adapted to provide multipoint multimedia communication services to a 
plurality of multipoint multimedia communication terminals, in broadband 
ISDN, and the method thereof. 
2. Description of the Prior Art 
Recently, multimedia services in the broadband ISDN have been further 
embodied to provide improved serviceable functions to users, as 
applications such as Asynchronous Transfer Mode (ATM) switches and 
transmission systems corresponding to a lower concept in the broadband 
ISDN have been broadly studied and Audio/Video compressed standard is 
determined by ITU-T, ISO/IEC. 
In future, various multimedia services may be extended to applications such 
as communication/distribution services, e.g., Video-On-Demand (which is 
referred to as "VOD" hereinafter) and interactive series, e.g., 
video-telephone and Tele-conference. 
The interactive multimedia communication services has been embodied 
recently by the ITU-T a standard for multimedia communication terminals 
with H.320 series available in various networks, based on H.261 image 
compression coding technique. In Digital Audio Video International Council 
(DAVIC), a standard of VOD type of service system have been defined 
through the use of the MPEG standard of ISO/IEC. In a type of the 
multimedia communication terminals, the interactive services employs the 
H.261 standard compression technique and the communication/distribution 
service applications such as the VOD incorporates the MPEG standard 
compression technique. On the other hand, various communication services 
and multimedia communication terminals, which is combined together with 
standards previously described, may be introduced as a terminal based on 
the MPEG standard of ISO/IEC is standardized by the ITU-T, and an 
interactive bi-directional communication service is utilized to the DAVIC 
and the like. 
More particularly, MPEG-2 in the ISO/IEC have being directly applied to 
service applications such as Cable Television (CATV), digital TV broadcast 
and the VOD, wherein the services is available in terms of Set-Top Box 
(which is referred to as "STB" hereinafter) already completed a 
specification and a standard. Such STM may be incorporated applications 
such as TV, Video Cassette Recorder (VCR) and Personal Computer (PC) which 
have broadspreadly been popularized to individual user. Based on the STB, 
users are capable of utilizing various multimedia communication services 
on the broadband ISDN on a real time basis. Provision of the interactive 
communication series such as video-telephone and Tele-conference to an 
user, however, is possible by using only H.320 terminals according to a 
type of corresponding network. As a result, there is a drawback that the 
users currently using such STB have to purchase the H.320 terminals to use 
the interactive communication services. In this case, therefore, an MPEG 
coding module is applied to the STB incorporating therein a network 
interface function and an MPEG decoder, thereby allowing the user to 
efficiently utilize the bi-directional multimedia communication service. 
In the multimedia communication terminals, various types of media signals 
and it combined signals may be utilized depending on service applications 
and characteristics of devices incorporated therein. The MCU for providing 
the multipoint multimedia communication service has a need of structure 
adapted to various media signal processing. To accomplish this, the 
present invention provides an MPEG based moving picture processing among 
various media signal processing functions. 
The conventional Multipoint Control Unit incorporating an image processor 
therein has two functions; i.e., one is a switching function of switching 
moving pictures generated from a plurality of multimedia communication 
terminals connected thereto to distribute to a preset location, and the 
other is a screen splitting function of allowing a multiplicity of input 
moving pictures to be displayed on a simple screen. 
In the screen splitting function, there is a merit that the MCU carries out 
the multiplicity of input moving pictures and transmits the same to each 
terminal, to thereby allow each terminal's user to concurrently see each 
of the input moving pictures on the same screen. Such screen splitting 
function is useful for multimedia communication service applications such 
as multipoint video-conference systems. Since, however, the conventional 
MCU incorporating the image processor therein mainly employs 
screen-splitting technique based on PEL (Pixel element) domain, which is 
provided with encoders and decoders corresponding to the number of 
input/output connection communication terminals, respectively, the MCU 
results in a completely structure. 
The conventional screen-splitting technique is based on a Transcoding 
technique, which is converts a compressed image inputted from the MCU into 
an image data on the PEL domain through the use of a moving picture 
decoder, and performs Scaling, filtering and reordering processes on a 
converted PEL image data, followed by a compression process using a moving 
picture encoder to thereby generate a compressed signal to be transmitted 
to video-conference participants terminals. In such transcoding technique, 
however, the moving picture signal can be adaptively treated, while an 
image processor with a complicated structure consisting of a number of 
decoders and encoders must be integrated on the MCU. 
In addition, an iterative performance of decoding and encoding processes 
results in a degradation in picture quality, i.e., degradation in a 
Quality of Service (QoS). 
Especially, QoS of the interactive communication service on a real-time 
basis has a limitation, due to a delay invoked by a buffer for 
transmitting output generated from an encoder with a traffic 
characteristic of variable bit in a constant bit rate, and a delay invoked 
during encoding and decoding processing. In case the transcoding technique 
is used for the screen-splitting function of the MCU, a total delay 
element induced by a sequence of a transmission terminal, a network, the 
MCU and a reception terminal, should be considered. 
In addition, the screen-splitting technique previously described has 
shortcomings that delay resulting from the iterative encoding and decoding 
operations prevents the multipoint multimedia Communication services from 
being provided to the users on the real time basis, wherein most of the 
delay is occurred between transmitting terminal and a receiving terminal 
except the MCU. 
Further, in the conventional screen-splitting technique which is not 
applied the decoding and encoding operations at the completely compressed 
domain, there has been studied only H.261 moving picture signals, but 
there have not been studied with respect to MPEG based on moving pictures, 
which is differed from compression manner for the H.261 and also encoding 
syntax configuration for moving pictures. 
SUMMARY OF THE INVENTION 
It is, therefore, a primary object of the present invention to provide a 
device which is capable of splitting a screen expressed in MPEG compressed 
moving pictures at a completely compressed domain, without the use of 
decoders and encoders, in broadband ISDN, to thereby reduce a degradation 
in picture quality resulting from the screen-splitting process, and also 
minimize delay invoked during the screen-splitting process based on 
non-transcoding technique, which in turn, lead to provide multipoint 
multimedia communication services employing therein Multipoint Control 
Unit (MCU) on a real time basis to users. 
In accordance one aspect of with the invention, there is provided a device 
for multiplexing N media signals fed from a plurality of multimedia 
communication terminals through broadband Integrated Service Distance 
Network (B-ISDN) to be displayed same on a display unit of the plurality 
of terminals, by using a Multipoint Cotrol Unit (MCU) wherein N being a 
positive integer, the device comprises: first network interface means for 
interfacing the N media signals from the plurality of multimedia 
communication terminals through the B-ISDN; pre-processing means for 
receiving the N media signals from the first network interface means, and 
demultiplexing the same into a preset number of streams with audio, video 
or data; a screen-splitting processing means for operating and reordering 
the preset number streams fed from the pre-processing means at a 
completely compressed domain to obtain a screen formed by the preset 
number streams, to thereby split the screen; a post-processing means for 
multiplexing the screen fed thereto from the screen-splitting processing 
means into N multiplexed screens corresponding to the terminals; and a 
second network interface means for outputting the multiplexed screens fed 
thereto from the post-processing means to the multimedia communication 
terminals, respectively. 
Preferably, the screen-splitting processing means includes input buffers 
for temporally storing the preset number stream fed thereto from the first 
network interface means; a screen operating/reordering block for 
sequentially retrieving each stream stored in corresponding input buffer, 
and operating and reordering the same in a frame arrangement order to 
generate a combined screen with moving pictures; and a output buffer for 
temporally storing the combined screen to be outputted to the 
post-processing means. 
In accordance with another aspect of the present invention, there is 
provided a method of multiplexing moving pictures fed from a plurality of 
multimedia communication terminals through broadband Integrated Service 
Distance Network (B-ISDN) and displaying a multiplexed moving picture on a 
display unit of the plurality of terminals, by using a screen-splitting 
device in a Multipoint Control Unit (MCU) including a first network 
interface circuitry for interfacing a plurality of media signals from the 
plurality of multimedia communication terminals through broadband 
Integrated Service Distance Network (B-ISDN); a pre-processor for 
demultiplexing the media signals fed thereto from the first network 
interface circuitry into a preset number of streams with audio, video or 
data; a screen-splitting processor for operating and reordering the preset 
number streams fed from the pre-processing means at a completely 
compressed domain to obtain a screen formed by the preset number streams, 
to thereby split the screen; a post-processing circuitry for multiplexing 
the screen fed thereto from the screen-splitting processing circuitry into 
N multiplexed screens corresponding to the terminals; and a second network 
interface circuitry for outputting the multiplexed screens fed thereto 
from the post-processing means to the multimedia communication terminals, 
respectively, wherein N being a positive integer, which comprising the 
following steps; checking a type and a performance of the terminals, and 
assistance possible performance of the MCU to the terminals by end-and-end 
signaling; and selecting M terminals among the plurality of terminals 
connected thereto; generating a start signal to the selected M terminals, 
the start signal allowing each of the selected terminals to generate the 
moving picture to be processed; processing a first and second moving 
pictures generated from two terminals in response to the start signal; 
processing a third and four moving pictures generated from two terminals 
in response to the start signal; repeating said steps until all of moving 
pictures from the selected M terminals are inputted. 
In addition, the step of processing the first and second moving pictures 
includes; modifying slice information contained in the first moving 
picture provided from the first terminal; deleting information for a 
sequence layer and a picture layer contained in a first Slice of the 
second moving picture, and newly modifying by a predetermined value a 
value of the MBAI which is a variable code of macroblock layer; appending 
a required stuffing bit to a new MBAI value to be matched a byte sequence 
of the code, as the MBAI value is varied; and checking whether both of the 
first and second moving pictures are completely processed, repeating the 
above steps until it are completely processed, if not so. 
Preferably, the step of processing the third and four moving pictures 
includes; deleting information for a sequence layer and a picture layer 
contained in a first Slice of the third moving picture, and newly 
modifying a value of Slice-Start-Code (SSC) to obtain a continuous slice; 
deleting information for a sequence layer and a picture layer information 
contained the four moving picture, and newly modifying both of the SSCI 
and MBAI values by a preset value, respectively; appending a required 
stuffing bit to a new MBAI value to be matched a byte sequence of the 
code, as the MBAI value is varied; and checking whether both of the third 
and four moving pictures are completely processed, repeating the above 
steps until it are completely processed, if not so. 
Preferably, the predetermined value used in modification of the MBAI values 
and the preset value used in modif ication of the SSC values are 
identically applied in next modification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, there is illustrated a schematic diagram showing a 
device of splitting image screens fed from a multiplicity of participant's 
terminals into a simple screen, when a number of terminals are connected 
to an Multipoint Control unit (MCU) for multipoint connection in broadband 
ISDN environment. 
When the number of terminals utilizing therein MPEG moving pictures 
compression technique are coupled with the MCU, the present invention 
selects four participants among the multiplicity of participants, receives 
moving pictures from each of the participant's terminals and performs the 
screen-splitting process. In this case, the multimedia communication 
terminals transmits moving pictures to the MCU in MPEG SIF format and the 
MCU provides screen-splitted pictures to the respective terminals in MPEG 
ITU-R BT601 format. 
Referring to FIG. 2, there is a block diagram of bi-directional multimedia 
communication terminals utilizing Digital Audio Video International 
Council (DAVIC) STB device, wherein an MPEG encoder may be provided 
therein through A0 interface inside the STB standardized by the DAVIC 
previously described, or an encoder 30 may be connected to an AAL layer 
12b within an Set-Top Unit (STU) 12. The STU 12 includes an ATM layer 12a, 
the AAL layer 12b, an MPEG demultiplexer 12c, an MPEG-2 decoder 12d for 
decoding audio/video signals inputted thereto from the MPEG demultiplexer 
12c, and an MPEG-1 decoder 12e. 
In case of the former, since a function module for an interactive 
multimedia communication is directly connected to a Cell bus 60 
corresponding to a Network Interface Unit (NIU) 11 containing only the 
physical layer, it suffers from the disadvantage that it must be 
incorporated therein functions for processing the ATM layer 12a and the 
AAL layer 12b in addition to the encoder 30. However, since signal format 
and connection manner of the A0 interface, which is defined at the STU 12 
are still employed as a correct signal format at the DAVIC, it is possible 
to overcome a problem of changing in an inner hardware structure of the 
STB. 
In the meantime, the latter is a method that the encoder 30 is directly 
coupled to the AAL layer 12b, while associated interfaces have not been 
currently defined on the DAVIC. However, in case the STB is integrated on 
universal personal computers, an MPEG encoder shown in FIG. 5 may be 
organized without the occurrence of any problem when a module having the 
MPEG encoder and a miltiplexer is installed on a slot of the PC and an 
AAL-5 is used for the data transmission thereof. the MPEG encoder 30 may 
be connected along two different paths, numbered 40 and 50 as shown In 
FIG. 2 depending on the installation position thereof. 
As described above, by adding MPEG-1 encoding function to the 
above-mentioned STB, users are capable of utilizing 
distribution/communication possible VOD services as well as the 
interactive communication services such as video-telephone and 
teleconference with lower cost. 
Referring to FIG. 3, there is shown a diagram depicting one-way delay 
elements generated between a transmission terminal and a reception 
terminal, during the video-conference communication in the broadband ISDN, 
wherein the total delay may be defined by a sum of delays in the 
transmission terminal, that in the reception terminal and that associated 
with the network. Recently, one-way maximum delay allowance value is 150 
ms. Considering delay invoked by a transmission buffer employed when the 
moving picture signals is transmitted at a constant bit rate format in the 
broadband ISDN, it is extremely impossible to guard the limited value, 
i.e., 150 ms, in an end-to-end signaling. 
Referring to FIG. 4, there is presented a diagram showing one-way delays 
passing the MCU, when terminals are connected to the MCU so as to 
implement the multipoint multimedia communication, wherein It would be 
understood that the end-to-end delay is greater than at least that shown 
in FIG. 3. In FIG. 3, in case a transcoding method is employed to 
implement screen-splitting functions of an image processing sector 
included in the MCU, it may be readily understood that the transcoding 
method has a substantial limit in the multipoint multimedia communication 
at a real time. Preferably, Functions of the screen-splitting processing 
sector of the MCU, therefore, requires nothing of delay elements. 
Referring to FIG. 6, there is presented a block diagram showing the MCU 
incorporating therein a screen-splitting device in accordance with the 
present invention, which comprises a first network interface circuitry 150 
for matching a number of multimedia signals, i.e., first input, second 
input, . . . , (n-1)th input, nth input, applied thereto through the 
broadband ISDN into signal of ATM networks; a pre-processing block 160 for 
demultiplexing Transport Stream (TS) consisting of a plurality of media 
signals multiplexed at MPEG-2 system (ISO/IEC 13818-1), or Program Stream 
(PS) consisting of a plurality of media signals multiplexed at MPEG-1 
system (ISO/IEC 11172-1) through the first network interface circuitry 
150, to sort out individual media signal such as audio and video signals, 
e.g., four media signals; a screen-splitting processor 200 for handling 
and reordering the four compressed media signals fed from the 
pre-processing block 160 at a completely compressed domain by using the 
non-transcoding method; a post-processing block 310, which acts a reversed 
function of the pre-processing block 160, for multiplexing moving picture 
signals processed in the MPEG ITU-R BT601 signal format and media signals 
inputted thereto from audio and video processors (not shown), and 
generating multiplexed media signals to be corresponded to the number of 
multimedia communication terminals connected thereto; a second network 
interface circuitry 320 for outputting the multiplexed media signals to 
multimedia communication terminals connected thereto through the ATM 
networks. The media signals fed to the corresponding multimedia 
communication terminals is thus decoded at the user's MPEG-2 decoder to be 
displayed on a display unit (not shown). 
More specifically, the pre-processing block 160 retrieves MPEG video 
Elementary Stream (ES) from the first network interface circuitry 150, 
which is inputted to four buffers, 210, 220, 230 and 240 in the 
screen-splitting processor 200. The pre-processing block 160 may be 
implemented through the application of end-to-end signaling (ITU-T H.245, 
ITU-T T.120 series) between the multimedia communication terminals in the 
user site and the MCU, or may be also implemented by selecting a 
particular speaker at an audio processor (not shown) and informing same to 
next processors. 
As shown in FIG. 6, the screen-splitting processor 200 includes the four 
buffers, 210, 220, 230 and 240, a screen handling/reordering block 250, 
and an output buffer 260. Specifically, the four buffers, 210, 220, 230 
and 240 temporally stores the four MPEG moving picture signals provided 
thereto from the pre-processing block 160, respectively. 
In this case, when there is three multimedia communication terminals, MPEG 
image compressed signal with a fixed image pattern is coupled to one of 
the buffers, i.e., a buffer whose input of the image compressed signal 
thereto is emptied, which may be read successively out for processing 
thereof. 
The screen handling/reordering block 250 retrieves successively the 
compressed image signal stored in for example, the buffer 210, and output 
sequentially it to the output buffer 260 to be stored therein, based on a 
frame arrangement order as shown in FIG. 7. 
When input to the buffer 210 is the compressed image signal corresponding 
to MPEG-1 SIF or MPEG-2 MP(SP)/LL formats shown in FIG. 7, and structure 
and synchronous of Group of Picture (GOP) in the compressed image signals 
inputted to each of the buffers 210, 220, 230 and 240 are identical from 
each other, the screen handling/reordering block 250 sequentially operates 
the compressed image signals, i.e., numbered 211, 212, 213 and 214, as 
shown in FIG. 7, stored in each of the input buffers, and reorders the 
compressed image signals 211, 212, 213 and 214, which is forwarded to the 
output buffer 260. 
The output buffer 260 temporally stores the compressed image signals 211, 
212, 213 and 214 extracted sequentially from the screen 
operating/reordering block 250 and then output the same to the 
post-processing block 310. 
Referring to FIG. 7, there is shown a diagram presenting how four MPEG SIF 
inputs, numbered 211, 212, 213 and 214 are combined to form a simple frame 
with MPEG ITU-R BT601 pattern. 
Referring to FIG. 8A, there is shown a diagram depicting a frame 
configuration for one of the MPEG-1 SIF inputs, e.g., 211, shown in FIG. 
7, wherein the frame is comprised of 240 lines each of which having 352 
pixels, the 240 lines including 15 Slices each of which having 16 lines, 
and each Slice is divided into 22 macroblocks, MB1, MB2, . . . , MB22 as 
shown in FIG. 8B. 
Referring to FIG. 9A, there is shown a diagram depicting configuration of 
the simple frame with MPEG ITU-R BT601 pattern as shown in FIG. 7, wherein 
the simple frame is comprised of 480 lines each of which having 740 
pixels, the 480 lines including 30 Slices each of which having 16 lines. 
and each Slice is divided into 44 macroblocks, MB1, MB2, . . . , MB44 as 
shown in FIG. 9B. 
Even though all possible frame configuration associated with the MPEG 
standard have not been offered, it may be understood that other frame 
configuration may be also summarized as FIGS. 9A and 9B. 
In FIG. 10, an MPEG Slice layer includes SSC (Slice Start Code), QC 
(Quantizer Scale Code), EBS (Extra Bit Slice), EIS (Extra Information 
Slice) and MS layer. In FIG. 11, an MPEG macroblock layer includes MS 
STUFF, MB ESC (Macroblock Escape), MBAI (Macroblock Address Increment), 
MBTYPE (Macroblock Type), QS (Quantizer Scale Code), MHF (Motion 
Horizontal forward Code), MVF (Motion Forward Code), MHB (Motion 
Horizontal Backward Cope), MVB (Motion Vertical Backward Code), CBP and 
Block layer. 
Referring to FIG. 12, there is shown a diagram explaining how the four 
compressed image signals 211, 212, 213 and 214 extracted from the input 
buffers 210, 220, 230 and 240 are processed by the screen 
operating/reordering block 250 in the screen-splitting processor 200 shown 
in FIG. 6 according to MPEG block configuration. 
The screen operating/reordering block 250 first retrieves the compressed 
image signal 211 from the input buffer 210, checks header information 
contained in each layer, and checks whether data on any layer currently 
have being inputted thereto. 
In the screen operating/reordering block 250, a first slice layer 
information of the compressed image signal 211 is fed to the output buffer 
260 without any operating therefor, and information of sequence and 
picture layers contained in the compressed image signals 212, 213 and 214 
are deleted to obtain a single MPEG compressed image signal. 
As the frame configuration shown in FIG. 7, Slice information of the 
compressed image signal 212 secondly fed is retrieved, and MBAI value of 
the macroblock layer is then changed to be identified as a macroblock 
contained in equal Slice. In this case, since the changed MBAI value is a 
code value obtained by the variable length coding, an optional stuffing 
bit may be added to the coded value so as to prevent arrangements of byte 
sequence of the MPEG compressed image signal from dispersing due to a 
change in the value. After Slice information (for maximum 15 slices) 
contained in each of the compressed image signals 211 and 212 are 
processed, the screen operating/reordering block 250 retrieves the 
compressed image signal 213 stored in the input buffer 230. Thereafter, a 
value of the SSC is modified to form continuous slices based on MPEG ITU-R 
BT601 pattern. Similar to the above procedure, Slice information contained 
in the compressed image signal 213 is detected and then the compressed 
image signal 214 stored in the input buffer 240 is retrieved for the 
processing thereof. 
In processing for the compressed image signal 214, values of the SSC and 
the MBAI are modified, and a required stuffing bit is added to the 
modified value. 
By iteratively performing the above step, the screen operating/reordering 
block 250 delivers a combined frame consisting of the four compressed 
image signals, 211, 212, 213 and 214 as shown in FIG. 7 to the output 
buffer 260, to be stored sequentially therein. 
The output buffer 260 generates the combined frame stored therein to the 
post-processing block 310. 
The post-processing block 310 multiplexes the combined frame fed thereto 
from the output buffer 260 and generates same to the second network 
interface circuitry 320. In the second network interface circuitry 320, n 
number of multiplexed outputs, are furnished to user's terminals connected 
thereto. 
Referring to FIG. 13, there is shown a flowchart explaining a method of 
splitting screen with the MPEG moving picture signals at the completely 
compressed domain, in accordance with a preferred embodiment of the 
present invention. 
First, the multipoint multimedia communication service is activated by the 
inventive MCU. User's terminal requires a virtual channel for 
end-to-network signaling, and the MCU sequentially is connected to a 
multiplicity of terminals. e.g., 4, through the virtual channel depending 
on a reservation. After an network connection between the MCU and the 
terminals is terminated. 
In step S1, negotiations between the MCU and the terminals is performed to 
check a type and a performance of the terminals, and assistance possible 
performance of the MCU to the terminals by the end-and-end signaling. In 
this case, Information necessary to the screen split processor 200 among 
the checked primary contents is an image compressed format information and 
a structure of the GOPs of the MPEG image, especially in case of the 
MPEG-1 SIF format, an agreement on which must be presented only one Slice 
an equal horizontal axis. In case MPEG-2, there is no the presence of one 
or more Slices on the equal horizontal axis. 
After the termination of the end-to-end signaling negotiation, if the 
negotiation condition is coincided from each other, the MCU generates a 
start signal to the four terminals connected thereto, the start signal 
allowing the four terminals to generate image compressed stream to be 
processed to the MCU. In response to the start signal, a first terminal 
generates the compressed image signal, followed by a second terminal, 
followed by a third terminal, and followed by a four terminal. In the MCU, 
vertical/horizontal information, i.e., 352/240 or 352/288, among Slice 
information of the compressed image signal to be first processed, are 
transformed into 704/480 or 704/576 corresponding to the MPEG ITU-R BT601, 
respectively. 
In step S3, the MCU vary an information field representing a compressed bit 
rate and that representing a capacity of the buffers for the compressed 
image signals based on the volume of the combined compressed image data, 
to thereby allow the MPEG-2 decoder to perform the decoding function 
thereof. 
After the above step, in step S4, information for a sequence layer and a 
picture layer contained in a first Slice of the compressed image signal 
secondly inputted are deleted. a value of the MBAI is then newly changed 
to MBAI+22. In a subsequent step S5, a required stuffing bit is appended 
to the new MBAI value to be matched a byte basis of the code, as the MBAI 
value corresponding to a variable code is varied. In step S6, the 
inventive screen-splitting device checks whether both of the first and 
second compressed image signals 211 and 212 are completely processed, 
wherein, the above steps S4 and S5 are repeated until the first and second 
compressed image signals 211 and 212 shown in FIG. 12 are completely 
processed, if not so. when processing for the first and second signals is 
terminated, the step proceeds to step S7. 
In step S7, a first Slice information of the compressed image signal 
thirdly inputted is detected and unwanted sequence and picture layer 
information contained therein are deleted, and the SSCI value is then 
newly changed to SSCI+15. In a similar manner, in step S8, a first Slice 
of the four compressed image signal 214 is retrieved and unwanted sequence 
and picture layer information contained therein are deleted to thereby 
modify both of the SSCI and MBAI values, i.e., "SSCI+15" and "MBAI+22", 
respectively. 
After the modification, in step S9, a required stuffing bit is appended to 
the MBAI value to be matched a byte basis of the code, as the MBAI value 
being the variable code is varied. Next, in step S10, it is checked 
whether the third and four compressed image signals, 213 and 214, are 
carried completely out, wherein the above steps S7 to S9 is repeated if 
the process for the compressed image signals, 213 and 214, is not 
terminated. and the step S10 proceeds to step S11 if the process is 
terminated. 
In step S11, it is checked whether all of compressed image signals are 
inputted, wherein the above step proceeds to step S3 if compressed image 
signals to be processed are presented, to thereby allow the remaining 
image signals to be processed, and the above step is ended if all of 
compressed image signals are completely processed. 
Specifically, if the termination of the screen-splitting process is 
required, or a currently inputted stream is detected as a final stream by 
analyzing header information of the input stream through the end-to-end 
signaling, while a procedure of splitting a consecutive moving picture 
screen is being performed in the compressed domain, then the 
screen-splitting process is ended to thereby stop all operation. 
According to the process mentioned above, one of the moving picture 
compressed frames is processed, followed by the remaining frames, to 
thereby render a screen-splitted image to be displayed on a display unit 
(not shown) of each user's terminal. 
Thereafter, virtual channels are switched through the end-to-end signaling 
and the end-to-network signaling, thereby being disconnected the 
multipoint multimedia communication terminal from the MCU to terminate the 
multimedia communication services. 
As previously mentioned, the present invention offers the following 
advantages. 
The present invention is first efficiently capable of splitting screen in 
the MPEG moving pictures, when the MPEG based compressed image signals is 
used in the multimedia communication terminals to implement the multimedia 
communication service such as a multipoint video-conference. 
In addition, in comparison with the prior art method, the present invention 
has a merit that the interactive multimedia communication service is 
possible to be provided users on a real time basis, and the structure 
thereof is less complex than those of the prior art device. 
Moreover, the present invention is capable of performing the 
screen-splitting function in the completely compressed domain without any 
degradation in the picture quality, and further minimizing a processing 
delay induced by the non-transcoding technique, to thereby allow the 
multimedia communication service to be implemented on a real time basis. 
To boot, in comparison with the prior art method, the invention has a 
simplified structure and improved characteristics, to thereby making it 
possible to achieve a reduction in the fabricating cost thereof. 
While the present invention has been described with respect to the 
particular embodiments, it will be apparent to those skilled in the art 
that various changes and modifications may be made without departing from 
the spirit and scope of the invention as defined in the following claims.