Abstract:
The present invention is a method and system for reducing delay in video communication, including, for example, video transcoding and continuous presence in a multipoint multimedia conference. The video communication control unit reduces such delay by processing a video stream in a small number of macroblocks referred to as “chunks,” without waiting to get a full frame of video data. Instead, the incoming video stream is converted into decoded chunks. These decoded chunks are transferred to an output module without waiting to decode an entire frame. An encoder in the output module encodes the decoded chunks (also referred to as encoder chunks), and transfers them to an end user without waiting for the entire frame to be processed. Thus, reducing the delay in waiting for the entire frame of video data provides improved real-time video communication.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of application Ser. No. 10/344,792, filed Jul. 30, 2003, now U.S. Pat. No. 7,535,485, which is a national stage filing of, and claims priority to, international application PCT/IL01/00757, filed Aug. 14, 2001, which in turn claims priority to U.S. provisional patent application Ser. No. 60/225,491, filed Aug. 15, 2000. The entire contents of each of these applications are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    This invention relates to the field of video communication and, more particularly, to providing real-time video conferencing while minimizing transmission and processing delays. 
         [0004]    2. Description of Background Art 
         [0005]    As the geographical domain in which companies conduct business continues to expand, video teleconferencing technology attempts to bring the world closer together. But, as with most user based technologies, users can be very critical and demanding with regards to the quality of the technology and the comfort of the user interface. One of the main complaints with regards to video communication technology is the delay that occurs between video streams sent between participants of the video conference. The delay tends to decrease the quality of the video communication experience as participants inadvertently start talking at the same time, yet are several words into the process before the conflict is realized. The greater the delay resulting from the processing or the transmission of data, the more difficult communication is between the participants. 
         [0006]    There are several factors that contribute to the delay in the video stream. One such factor arises when the encoding of the video streams is performed at user or participant terminals where the video stream is created. Another such factor arises simply due to transmission delays that accrue when transmitting the encoded video stream through a network to a Video Communication Control Unit (VCCU), like but not limited to, a Multipoint Control Unit (MCU), a Multimedia Gateway, etc. Typically, a VCCU serves as a switchboard and/or conference builder for the network. In operation, the VCCU receives and transmits coded video streams to and from various user terminals or codecs. 
         [0007]    Another contribution to the delay of the video stream is due to the processing performed on the encoded video stream within the VCCU. Once the VCCU completes its processing of the video stream, additional delays are incurred while the processed video stream is transmitted through the network to target user or participant terminals. After the participant terminals receive the video stream, additional delays are caused by the decoding of the encoded video streams back to normal video. 
         [0008]    The VCCU may be used in several modes, such as video switching, transcoding, and continuous presence. In video switching, the VCCU serves as a switchboard, and the video stream is directly transmitted from a source terminal to a target terminal. In video switching operation, the input stream is passed through the VCCU, and the VCCU is not required to perform any video processing. Although video switching achieves a reduction in the delay of the video stream, it is not adequate to solve the present problem because, in many situations, video switching cannot be utilized. Two such situations arise where transcoding is required or a continuous presence mode of operation is provided. 
         [0009]    Transcoding of the video stream is required when the input stream does not match requirements of the target user terminal (such as bit rate, frame rate, frame resolution, compression algorithm, etc.). Transmission of the video streams in this mode requires video processing, which may result in delays due to the required processing time, and thus, a less than optimal video conference. 
         [0010]    Continuous presence (“CP”), involves video mixing of the video data from various source user terminals, thus resulting in a need for video processing. Both transcoding and the continuous presence mode cause delays in the delivery of video streams within a video communication system. Thus, it is evident that there is a need in the art for a technique to eliminate or alleviate the delays in the video stream to improve the video communication experience. 
         [0011]    The elaborate processing required in transcoding and continuous presence operation must be done under the constraint that the input streams are already compressed by a known compression method based on dividing the video stream into smaller units, such as GOP (group of pictures), pictures, frames, slices, GOB (Group Of Blocks), macro blocks (MB) and blocks as described in standards such as the H.261, H.263, and MPEG standards. 
         [0012]    A typical VCCU, like the MGC-100 manufactured by Polycom Networks Systems, contains a number of decoders and encoders. Each decoder receives a compressed stream of a known compression format, and decodes or uncompresses the compressed stream. The uncompressed frames are then scaled and rearranged to form a desired output layout. The resulting frame is then appropriately compressed by the encoders and transmitted to the desired target terminals. 
         [0013]      FIG. 1  is a block diagram illustrating a typical embodiment of video ports within a VCCU  100 . Two video ports are illustrated by way of example and for convenience of presentation; however, those skilled in the art will realize that the VCCU  100  can have many such video ports. The VCCU  100  receives compressed video streams from various terminals and places the compressed video streams onto a backplane bus  140 . Each video port  130  within the VCCU  100  is dedicated to one end terminal. Uncompressed video is shared through a dedicated video bus  150 , capable of transferring high bandwidth video streams at given maximum resolution under the maximum frame rate. 
         [0014]    The description of the present invention refers to a terminal in several names like: end terminal, terminal, end-point, endpoint, and end user terminal. In general, a terminal is an endpoint on the network that provides for real-time, two-way communications with another terminal, Gateway, or Multipoint Control Unit. This communication consists of control, indications, audio, moving color video pictures, and/or data between the two terminals. A terminal may provide speech only; speech and data; speech and video; or speech, data, and video. 
         [0015]    Once a compressed video stream from an end user terminal is placed onto the backplane bus  140 , the video stream begins to accumulate in an input buffer  125  before being provided to a decoder  120 . The decoder  120  converts the compressed video stream into uncompressed frames, and the uncompressed frames are placed into input triple frame memory  123 . The input triple frame memory  123  consists of three frame buffers. Working in a cyclic mode, one buffer is needed for the frame constructed by the decoder  120 . The second buffer is used for transmission over the video bus  150 . When the decoder  120  yields a full frame in the middle of a frame cycle (i.e., the transmitted frame buffer has not completed the transmission of its current frame), an additional buffer is needed to prevent stalling of the decoder  120 . 
         [0016]    The uncompressed frame transmitted from the input triple frame memory  123  is scaled according to the desired output layout by input scaler  127 , and then placed onto the video bus  150 . The appropriate video ports  130  then retrieve the scaled frame from the video bus  150 , using builder  112 , based on the layout needed to be generated. The builder  112  collects one or more frames from at least one video port as needed by the layout, and arranges the frames to create a composite output frame. An output scaler  117  then scales the composite frame to a desired resolution and stores the scaled composite frame in an output triple frame memory  115 . 
         [0017]    The output triple frame memory  115  consists of three frame buffers. Working in a cyclic mode, one buffer is needed for the frame received from the video bus  150 . The second buffer is used for the frame being encoded by an encoder  110 . When the encoder  110  receives a new frame from the video bus  150  in the middle of a frame cycle (i.e., the encode frame buffer is still busy), the frame is stored in this third buffer to prevent loss of the frame. The encoder  110  then encodes the frame from the output triple frame memory  115 , and stores the compressed data in an output buffer  113 . The data residing in the output buffer  113  is then transferred to the backplane bus  140 , and ultimately to the end user terminal. 
         [0018]    In the above description there is a total separation between the encoders and the decoders. The reason for this separation can typically be attributed to using off-the-shelf encoders/decoders, such as an 8×8 VCP processor, which were originally designed for use within end-points. The use of such off the shelf components forces the designer to design the video bus  150  as a video screen for the decoder and as a video camera for the encoder with video signals such as horizontal sync and vertical sync. The decoders output a newly uncompressed frame only when it was completely decoded. The encoders use the scaled frames only after the frame is fully loaded into their memory. 
         [0019]      FIG. 2  illustrates resulting delays in a typical video conference where two endpoints are connected to each other through a common VCCU. End-user A  25  transmits at a maximum frame rate of 30 frames per second (“fps”) while end-user B  21  transmits at a maximum of 15 fps. The first decoded MB of each incoming frame waits in the input triple frame memory  123  ( FIG. 1 ) until the whole frame received from the backplane bus  140  ( FIG. 1 ) is fully decoded. This process results in a delay of one input frame. Additionally, the decoded frame is delayed until the start of the next video bus frame cycle before being transmitted along with the rest of the frame to the video bus  150  ( FIG. 1 ), contributing an average delay of half a bus frame. The resulting delay to the decoder can be calculated by the following equation: 
         [0000]      DecoderDelay=1/InputFrameRate+1/(2*VideoBusFrameRate) 
         [0020]    Next, the encoder path of the video port  130  ( FIG. 1 ) retrieves the entire frame residing on the video bus  150 , and stores the frame into the output triple frame memory  115  ( FIG. 1 ). Additionally, the first MB is delayed until the encoder  110  ( FIG. 1 ) is ready to start encoding a new frame ( 27  for user A and  29  for user B). The average delay is therefore: 
         [0000]      EncoderDelay=1/VideoBusFrameRate+1/(2*OutputFrameRate) 
         [0021]    The total delay resulting from video sharing over a dedicated video bus simulating a screen on one side (decoder side) and a camera on the other side (encoder side) is: 
         [0000]      Delay=1/InputFrameRate+3/(2*VideoBusFrameRate)+1/(2*OutputFrameRate) 
         [0022]    Thus, it is evident that current technology utilized in multimedia video conferences results in significant video delays. In low frame rate connections, this delay can amount to a few hundreds milliseconds. This creates a significant degradation in the quality of the conference when considering that the delay is caused at both endpoints, and is typically of the same magnitude. Therefore, there is a need in the art for a method and system for reducing the delay in video transcoding and continuous presence for video conferencing technology. 
         [0023]    Prior art systems offer an approach to reduce the delay, however communication is limited. For example, prior art terminals have to use the same standard, or one layout (e.g., Hollywood Square, the screen is divided into four pictures of the same size) with QCIF to CIF Resolution. The present invention overcomes these limitations in that it can operate in several resolutions simultaneously, with any number of participants, as well as other layouts and standards. 
       SUMMARY OF THE INVENTION 
       [0024]    The present invention solves the above-described problems by providing a system and method for reducing delays resulting from video transcoding and continuous presence. In general, the present invention removes the need to delay processing video data until an entire frame is received. Instead, the system processes an incoming data stream in pieces (or “chunk by chunk”), thus reducing delays from waiting for the entire frame, and thereby improving quality of a video conference. 
         [0025]    More particularly, the present invention includes a video processing system that provides an improved real-time performance in processing video data streams. The video data streams are typically composed of a series of frames with each frame consisting of a plurality of blocks. Rather than processing the video stream on a frame by frame basis, the present invention achieves a shorter delay by processing the video data stream on a segment by segment of a frame basis. The system includes video input modules that receive video input streams from associated source endpoints. Each of the video input modules is coupled to video output modules through a common interface. The video input modules receive a compressed video input stream from the source endpoints, decode the compressed video input stream in small units (i.e., chunks), such as a few MBs, without waiting to get a full frame, and transfer the chunks of uncompressed data to the common interface before a full frame is accumulated. The video output modules receive the chunks of uncompressed data from the various input modules via the common interface, and build the required layout from the uncompressed data in a memory, which resides in the output modules. An encoder then encodes chunks of uncompressed data, from the memory, to create chunks of compressed video data. These chunks of compressed video data are then output for transmission to a target end point before a full frame is accumulated. 
         [0026]    In a particular embodiment of the present invention, an incoming compressed video data stream is received by an input module from a backplane bus. This data is converted by a chunk decoder located in the input module into decoded chunks, and pixel data corresponding to each decoded chunk is stored in memory. 
         [0027]    An output module retrieves the uncompressed chunks from the common interface. The output module contains an editor module, which retrieves the uncompressed chunks and stores these chunks into chunk buffers. The input data is written from the various chunk buffers into an input memory of the editor in the appropriate location. Concurrently the chunk to be encoded is read from the memory and processed by the chunk encoder. Once the outgoing compressed video chunk is generated, the chunk is transferred to a backplane bus in the VCCU. This process, by simultaneously writing the input data to the input memory of the editor and reading the appropriate chunk to be encoded from the memory, provides the most current information to the chunk encoder. 
         [0028]    Thus, the present invention advantageously processes the video data stream in a video communication system to reduce delays while providing optimal transmission for a video conference with improved real-time performance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a block diagram of a prior art video communication control unit (VCCU); 
           [0030]      FIG. 2  is a timing diagram illustrating resulting delays in a typical conference where two endpoints are connected to each other through the prior art VCCU; 
           [0031]      FIG. 3  is an exemplary embodiment of a video section of a VCCU, according to the present invention; and 
           [0032]      FIG. 4  illustrates a flow of video streams in an exemplary embodiment utilizing four memory maps corresponding to four input modules of the  FIG. 3  VCCU and a memory map corresponding to an output module of the  FIG. 3  VCCU, according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    Turning now to the figures in which like numerals represent like elements throughout the several views, exemplary embodiments of the present invention are described. Although the present invention is described as utilizing a video conferencing system, those skilled in the art will recognize that the present invention may be utilized in any sort of system with an incoming data stream which may be distributed to end users. 
         [0034]      FIG. 3  illustrates an exemplary embodiment of a video section of a VCCU  200 , according to the present invention. In the exemplary embodiment, an input unit  220  (also referred to as an input module) and an output unit  240  (also referred to as an output module) are connected to a backplane bus  210 . Although  FIG. 3  shows only one input module (i.e.,  220 ) and one output module (i.e.,  240 ), the scope of the present invention covers any number of input and output modules. The backplane bus  210  may be any type of a bus or transmission medium. The input module  220  and the output module  240  also interface through a common interface  230 . In  FIG. 3 , a compressed video signal  211  is sent via the backplane bus  210  to the input module  220  in the VCCU  200 . The input module  220  in turn routes the compressed video signal  211  (also referred to as an incoming video data stream) to a chunk decoder  221 . 
         [0035]    The chunk decoder  221  is a logical unit capable of processing a macroblock (MB) or any number of consecutive MBs (i.e., a chunk) from the incoming video data stream. Each chunk is decoded and forwarded for further processing without the need to wait for a whole frame to be constructed. The video is processed “chunk by chunk” and transmitted to a target via an input scaler  223  or directly to a chunk buffer  224  if scaling is not required. 
         [0036]    The chunk decoder  221  takes the received compressed video stream  211  and based on a reference frame memory  222   a  and encoding standards (H.261, H.263 etc.) converts it into decoded data. The decoded data can be either represented in an image (spatial) domain, in the DCT domain, or some variation of these or other techniques. The chunk decoder  221  stores the decoded data representing a decoded chunk into appropriate addresses of a new frame memory  222   b . This process overwrites any previous data stored in the appropriate addresses of the new frame memory  222   b . When the chunk decoder  221  completes decoding the data of an entire decoded chunk, it sends an indication to the scaler  223  using a decoded chunk data ready line  226 . 
         [0037]    When the chunk decoder  221  finishes decoding a frame, and before the arrival of a first chunk of a next frame, the decoded data from the new frame memory  222   b  is transferred to the reference frame memory  222   a  in one embodiment of the invention, or memories  222   a  and  222   b  swap pointers in an alternate embodiment of the invention. After updating the reference frame memory  222   a , the chunk decoder  221  is ready to start decoding the first chunk of the next frame. 
         [0038]    Upon receiving the indication via the decoded chunk data ready line  226 , the scaler  223  retrieves the appropriate decoded data from the new frame memory  222   b , scales it, and transfers the scaled decoded data (also referred to as a scaled decoded chunk) to a chunk buffer  224 . Using this method, the scaler  223  always uses the newest available decoded data. This method enables piecewise decoding, chunk by chunk, of the compressed video stream  211 , piecewise scaling, and transference of corresponding uncompressed data to the common interface  230  without waiting to accumulate a full frame. Using this method reduces delay in the input module  220  of the VCCU  200 . 
         [0039]    The purpose of scaling is to change frame resolution according to an endpoint requirement or in order to later incorporate the frame into a continuous presence layout. Such a continuous presence frame may consist of a plurality of appropriately scaled frames. The scaler  223  may also apply proper filters for both decimation and picture quality preservation. 
         [0040]    In some embodiments of the present invention, size of a decoded chunk and a scaled decoded chunk depends on a required scale factor. For example, when the video resolution needs to be reduced to a quarter (a factor of 2 in both axis), for a layout of 2×2 sources of video, the size of the decoded chunk may be two lines of MBs and the scaled decoded chunk size may be one MB. In case of a layout of 3×3 sources of video, the decoded chunk size may be three lines of MBs and the scaled decoded chunk size may be one MB. 
         [0041]    In some exemplary embodiments, the decoded chunk may comprise a few MBs and the scaled decoded chunk may comprise a few pixels. The scaler  223  retrieves decoded data, corresponding to a new decoded chunk, from an appropriate location of the new frame memory  222   b . This decoded data may also include a group of surrounding pixels needed for the scaler operation. The number of such pixels and their location within the frame depends on the scale factor, the filters, and a scaling algorithm that the scaler  223  is using. The scaler  223  always uses and processes decoded data which belong to a new decoded frame. Other embodiments may use various sizes for the decoded chunk and for the scaled decoded chunk. 
         [0042]    The scaler  223  may be bypassed if the scaling operation is not required in a particular implementation or usage. In such a case, a decoded chunk replaces a scaled decoded chunk for the rest of the process. 
         [0043]    The scaler  223  sends the scaled decoded chunk to the chunk buffer  224 . In one embodiment the chunk buffer  224  is a two stage FIFO style memory element. Thus, the chunk buffer  224  has capacity to store two scaled decoded chunks. However, the configuration of the chunk buffer  224  depends on a configuration of the common interface  230 . The common interface  230 , which routes the video data between input modules and output modules, (such as the input module  220  and the output module  240 ), can be a shared memory, a TDM bus, an ATM bus, a serial bus, a parallel bus, a connection switching, a direct connection, or any of a variety of other structures. 
         [0044]    In operation, the input module  220  sends a scaled decoded chunk to the common interface  230  via a line  231 . The common interface  230  then routes the scaled decoded chunk to the output module  240 . The VCCU  200  can have more than one output module  240 , and the scaled decoded chunk can be routed to more than one output module. 
         [0045]    The output module  240  includes an editor  250 . The editor  250 , in the appropriate output module  240 , retrieves scaled decoded chunks via a line  232  from the common interface  230  through a chunk buffer  251 . In one embodiment, the chunk buffer  251  is a two stage FIFO configured to store two scaled decoded chunks. The configuration of the chunk buffer  251  depends on the configuration of the common interface  230 . As shown in  FIG. 3 , any number of chunk buffers  251  may be embodied in the output module  240 . 
         [0046]    The editor  250  manages uncompressed input video data that can originate from various sources. The editor  250  is comprised of the chunk buffers  251  that take or receive scaled decoded chunks from one or more input modules  220 , and place the appropriate scaled decoded chunks in appropriate locations within an editor input memory  253  in order to compose a desired layout. In one embodiment, the editor input memory  253  contains a frame structure with specific locations corresponding to locations in a layout of a receiving endpoint. The frame structure may be single sourced, or it may be a composite sourced frame receiving data from various sources. 
         [0047]    In an alternative embodiment, the editor input memory  253  is allocated a frame structure for each source. A scaler  254  retrieves data from the editor input memory  253  based on the layout. In this case, layout composition will be implemented on-the-fly from the editor input memory  253  to a chunk encoder  241  by the scaler  254 . 
         [0048]    The present invention simultaneously writes data from the appropriate chunk buffers  251  into the editor input memory  253  overwriting any old data. Concurrently, the present invention reads the appropriate chunk that has to be encoded from the editor input memory  253  via the scaler  254  to the chunk encoder  241 . Using this method, the chunk encoder  241  always uses the newest available data for a current pixel in a sequence. Therefore in some cases, two adjacent pixels may come from two consecutive frames. 
         [0049]    The present invention enables piecewise encoding, chunk by chunk, of the uncompressed video input data, and piecewise transference of the compressed data to the backplane bus  210  without waiting to accumulate a full frame to which the uncompressed video data belongs. Thus, the present invention reduces delay in the output module  240  of the VCCU  200 . 
         [0050]    The video data may be scaled (applying a suitable filter for decimation and quality) with the scaler  254 , or various video inputs may be combined into one video frame by reading and transferring encoded chunks from appropriate locations in the editor input memory  253  according to a predefined or user defined layout scheme. The scaler  254  may be bypassed or not present in certain embodiments not requiring a composition function or scaling. By using the above method the editor  250  provides the most updated data to the chunk encoder  241 . 
         [0051]    It should be noted that the size of an encoded chunk can be different from the size of a decoded chunk or a scaled decoded chunk. In addition, the size of a decoded chunk or a scaled decoded chunk may be different for each of the decoders that participates in a conference. 
         [0052]    The output module  240  also comprises an editor control  252  and a rate control  243 . The editor control  252  is responsible for managing the operation of the editor  250 . The rate control  243  controls a bit rate (i.e., a data rate) of an outgoing video stream. 
         [0053]    The chunk encoder  241  essentially performs an inverse operation of the chunk decoder  221 . The chunk encoder  241  retrieves encoder chunks (i.e., scaled decoded chunks) from the editor  250 . Then, based on a content of a reference frame buffer  242   a  and the information supplied by the rate control  243 , the chunk encoder  241  generates a compressed video stream and transfers the compressed video stream to the network via the backplane  210 . From each compressed chunk (i.e., encoder chunk), the chunk encoder  241  decodes the compressed chunk, performs inverse transformation over the compressed chunk, and stores the results in a new frame buffer  242   b . The generation of the new frame buffer  242   b  and the outgoing video stream is based on the chosen standard (e.g., H.261, H.263 etc.). In another embodiment of the present invention, the editor  250  transmits each relevant chunk of data to the chunk encoder  241 . 
         [0054]    When the chunk encoder  241  finishes encoding an entire frame, and before arrival of a first chunk of a next frame, the data from the new frame buffer  242   b  is transferred to the reference frame buffer  242   a . Alternatively, the new frame buffer  242   b  and reference frame buffer  242   a  replace tasks by switching pointers. After updating the reference frame buffer  242   a , the chunk encoder  241  is ready to encode the first chunk of the next incoming frame. 
         [0055]      FIG. 4  illustrates a flow of video streams utilizing four memory maps  420  corresponding to four input modules  220  ( FIG. 3 ) and a memory map  430  corresponding to the output module  240  ( FIG. 3 ). In this example, the present invention is using the scaler  223  ( FIG. 3 ) of the input module  220  while the scaler  254  ( FIG. 3 ) of the output module  240  is bypassed. 
         [0056]    Various chunks,  4111 - 4114 , are received by the input modules  220  (independently for every source). Each chunk  4111 - 4114  is decoded into pixels by the chunk decoders  221  ( FIG. 3 ). These pixels are saved to the new frame memory  222   b  in specific addresses chosen according to the pixels&#39; coordinates. For instance, for a first of the four input modules  220  corresponding to a first memory map  420 , a received chunk  4111  is stored in memory location  415  (marked with stripes) of the first memory map  420 . The pixels constituting an entire frame are saved in the new frame memory  222   b  in an address range  410   a ; one address range per source. The address range  410   a  may contain information from two consecutive frames of the same source. The shaded area, which is before the memory location  415 , corresponds to the frame that is currently being decoded, while the white area, which is after the memory location  415 , corresponds to a previous decoded frame. In some embodiments, it is possible to save side information (e.g., quantizer, motion vectors, MTYPE, MB type etc.) for supporting the encoding process. 
         [0057]    The chunk decoder  221 , upon finishing decoding the current chunk  4111  and saving the decoded chunk to the memory location  415 , indicates via the decoded chunk data ready line  226  that the scaler  223  may start to process the new data (i.e., the decoded chunk). The scaler  223  retrieves the appropriate decoded pixels from the memory location  415  according to a scale factor and any filters that may be used. The scaler  223  then filters and down samples these pixels, possibly using other pixels located near the decoded pixels which belong to the new frame in the filtering process. Ultimately the results are available on the common interface  230  ( FIG. 3 ) and saved in the editor input memory  253  ( FIG. 3 ) of the output module  240  in a location  421  of the memory map  430 . 
         [0058]    The scaled frames from all the decoders  221  are saved in an address range of the memory map  430  (TL, TR, BL, BR) of the output module  240 , which, is divided into four quarters. In this exemplary embodiment, a Top Left (TL) quarter is used by the first of the four input modules  220  corresponding to the first memory map  420 . A Top Right (TR) quarter is used by a second of the four input modules  220  corresponding to a second memory map  420 . A Bottom Left (BL) quarter is used by a third of the four input modules  220  corresponding to a third memory map  420 , and a Bottom Right (BR) quarter by a fourth of the four input modules  220  corresponding to a fourth memory map  420 . When the chunk encoder  241  ( FIG. 3  and  FIG. 4 ) transmits an encoded chunk  445 , it takes appropriate pixel data from the address range of the memory map  430  (TL, TR, BL, BR) of the output module  240  (e.g., an address area  435  of the editor input memory  253 , which is the most current data available for a needed location in a layout). Next, the pixels associated with the address area  435  (encoder chunk) are taken by the chunk encoder  241 , and encoded (compressed) with or without using side information saved by the decoders  221 . The compressed data corresponding to the address area  435  are then transferred to an endpoint. 
         [0059]    Overall, this invention will improve the quality of video communication by reducing the delay resulting from the VCCU  200  ( FIG. 3 ) waiting to receive a full frame before processing the video stream. Reducing these processing delays will provide a higher quality video conference and will improve the real-time performance between the participants. Thus, this invention will be useful because of the increasing dependence on video communication technology, and the need to improve video stream processing to create a conference as life-like as possible. 
         [0060]    In the description and claims of the present application, each of the verbs, “comprise” “include” and “have”, and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements, or parts of the subject or subjects of the verb. 
         [0061]    The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments will occur to persons of the art. The scope of the invention is limited only by the following claims.