Abstract:
A video teleconferencing system and method transfers video teleconferencing signals from a sender to a receiver. The sender determines decision information based on internal or external factors. The sender may or may not generate a video teleconferencing signal depending on the content of the decision information. If generated, the video teleconferencing signal is encoded at the sender and sent to the receiver. Each sender includes at least one memory module for storing the decoded signal, each memory module is one group. The sender updates its memory module with a copy of each sent video teleconferencing signal. The receiver decodes the signal and presents the signal to the user of the receiver. The receiver stores a copy of the signal in a memory module identified with each specific sender.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority, under 35 U.S.C. § 119(e), from U.S. Provisional Patent Application Serial No. 60/218,073, “Video Teleconferencing Using Distributed Processing,” by Parry and Tan, filed Jul. 12, 2000, the entirety of which is herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to multipoint conferencing, for example, multipoint videoconferencing between multiple participants. More particularly, the invention relates to multipoint videoconferencing in which the computer processing used to implement various conferencing functions is distributed among the conferencing terminals used by the conference participants. 
     2. Description of the Related Art 
     As the result of continuous advances in technology, videoconferencing is becoming an increasingly popular means of communication. The development and standardization of advanced coding/decoding and compression/decompression schemes has facilitated the communication of ever larger amounts of information over communications links of limited capacity. Technological advances in the communication links themselves and increases in the sheer number of links have further increased the effective number of communications links that are available to carry videoconferencing information. Advances in the basic components used in videoconferencing systems, such as computers, cameras, video displays, audio speakers and microphones, have resulted in the availability of better quality components at lower prices. 
     These advances translate to more powerful videoconferencing systems available at lower prices. Video and audio quality has improved, as has the capability to combine the basic videoconferencing functionality with other functionalities, such as presentation software, desktop publishing applications, and networking. As a result, videoconferencing systems have progressed from being expensive novelty systems, which were used infrequently, to moderately priced systems which were more often used but still located in a dedicated facility shared by many users, to relatively inexpensive systems, which one day may be as ubiquitous as the telephone is today. 
     Current videoconferencing systems may be operated in a point-to-point mode between users of videoconferencing terminals or may include a number of clients connected to each other by a centralized multipoint control unit (MCU). The clients are the local systems used by the participants in the videoconference. Much, if not all, of the videoconferencing functionality is typically implemented by the MCU. As a result, the MCU is often a complex and expensive piece of equipment. For example, current MCU&#39;s may implement half of the signal processing and all of the decision making required to implement a videoconference. The MCU may be required to decode audio signals received from each client, mix the received audio signals together to generate appropriate audio signals to be transmitted to each client, and then re-encode and retransmit the appropriate mixed signal to each client. The MCU may perform analogous functions on the video signals generated by each client. Furthermore, the MCU typically also determines, according to some predefined method, which video signals (or which combinations of video signals) should be sent to which clients. As the number of clients increases, the functions required of the MCU increase correspondingly, quickly making the MCU prohibitively complex and expensive. 
     Note that in the above scenario, the audio signals and possibly also video signals experience both tandem encoding and multisource encoding, each of which reduces the quality of the signals. Tandem encoding means that a signal has been repeatedly and sequentially encoded and decoded. Here, the source client encodes its audio signal, which is decoded and mixed by the MCU. The MCU then encodes the mixed signal (i.e., tandem encoding), which is decoded by the destination client. Since the encoding algorithms used typically are lossy (i.e., the recovered signal is not a perfect replica of the original signal), each time a signal is encoded and decoded the quality of the signal decreases. Tandem encoding introduces significant delay and impairs natural communication. Multisource encoding of the audio signal is the encoding of an audio signal produced by more than one source (i.e., a mixed signal). Because the encoding algorithms typically are optimized for single source signals, encoding a signal from more than one source also results in a lower quality signal. 
     If the MCU is also responsible for determining which signals are to be mixed and sent to which clients, it typically must receive audio and video signals from all of the clients and then determine what to do with these signals. For example, with respect to video which is transmitted in packets, the MCU is continuously receiving video packets. Once the MCU has received these video packets, it must determine which of these video packets to forward to destination clients. This determination in its own right may be computationally intensive. The video packets that are not mixed or forwarded are simply discarded by the MCU and need not have been transmitted to the MCU in the first place. The transmission of video packets not required by the MCU creates unnecessary traffic on the network, thus wasting valuable bandwidth and unnecessary encoding work in the sending client. 
     Another approach to videoconferencing is to have each client indiscriminately broadcast its audio and video signals to all other clients. Because each signal goes directly to all other clients without any intermediate decoding, mixing or re-encoding, this method eliminates the need for tandem encoding and multisource encoding. However, continuously encoding, sending, receiving, and decoding video and audio signals from all clients to all other clients taxes both the network and the clients, particularly as the number of clients increases. 
     In view of the foregoing discussion, there is a need for a videoconferencing system that reduces or eliminates the cost of the MCU function. There is also a need for a videoconferencing system that does not require tandem encoding and/or multi-source encoding. There is a further need for a videoconferencing system that does not indiscriminately send video packets, but rather sends video packets only (or preferably) when they are to be received and utilized by other clients. There is also a need for a videoconferencing system that can accommodate an increased numbers of clients on a given network. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a videoconferencing system, method and apparatus that may take advantage of distributed processing techniques. In a preferred embodiment, the system includes two or more apparatus connected via a network in order to transfer video and audio signals. A sending client can apply various internal and/or external factors to a decision algorithm. Based on this algorithm, the sender decides whether to generate and send video and/or audio signals. Because the decision to send signals is made locally at the sender, all signals generated and sent, preferably, will be received and utilized by at least one receiving client. Each sender encodes the signal it generates before it sends the signal. This signal is then decoded at the receiver, preferably without any intermediate decoding or encoding. 
     Each sending client may include multiple decoders and memory modules such that the client can store a copy of the signals sent to each receiver. As a result, the sending client can compare the current image with the immediately preceding image that was sent to any particular receiving client. If there was no change, then no new image need be sent; otherwise only a difference signal is sent, thus increasing the overall efficiency of the videoconferencing system. 
     Similarly, each receiving client may include multiple decoders and memory modules, such that the receiving client can store a copy of the signals, if any, received from each sender. As a result, the receiving client can, either manually under command from a user or based upon an automated decision algorithm, display the audio and/or video signals from various senders. Preferably, of course, in order to conserve bandwidth, each receiving client sends a command instruction to each sending client instructing them not to send any signals if the same will not be displayed and played at the receiving client. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention has other advantages and features that will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is an illustration of a preferred embodiment of a system including the present invention; 
     FIG. 2 is a block diagram of one embodiment of a sending client; 
     FIG. 3 is a block diagram of one embodiment of a receiving client; 
     FIG. 4 is a flow diagram of preferred embodiment of a sending process; and 
     FIG. 5 is a flow diagram of a preferred embodiment of a receiving process. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is an illustration of a preferred embodiment of a system including the present invention. The system includes a network  102  and at least two clients  104 . The clients  104  are each connected to the network  102 . The network  102  may be an intranet, the Internet, a local area network, a point-to-point connection, or any other means of connecting two or more videoconferencing units together for the purpose of sending and receiving audio and video signals. The client  104  is a videoconferencing terminal. In a preferred embodiment, some clients  104  are both a sender and receiver of audio and video signals. Client  104  may have any number of configurations of audio and video equipment to facilitate sending or receiving audio and video signals. For instance, in one embodiment, client  104  may include a video display unit, an audio speaker, a camera, a microphone and a processing unit running suitable software for implementing the videoconferencing functionality discussed in greater detail below. In this embodiment, the video display unit and speaker are used by the receiving portion of the client to present the received sounds and image signals to the user. The camera and microphone are used by the sending portion of the client to create the video and audio signals sent by the client. The client  104  uses the processing unit in both the sending and receiving processes. 
     FIG. 2 is a block diagram of one embodiment of a sender or sending client  200 . In this embodiment, the sender or sending client  200  includes input devices  203 , a signal generator  204 , a decision module  202 , at least one encoder  206 , at least one reference memory  210 , at least one decoder  208 , and a sending module. The signal generator  204  is connected to the input devices  203 , the decision module  202 , and the encoders  206 . Each encoder  206  is also connected to a reference memory  210 , a decoder  208 , and the sending module  212 . Each decoder  208  is also connected to a reference memory  210 . The sender  200  is the portion of the videoconferencing client  104  that is responsible for sending audio and video signals. 
     The input devices  203  are used to create the video and audio signals. In a preferred embodiment, the input devices  203  include at least one camera and microphone. The input devices  203  may also include devices such as document readers, VCRs, DVD players, application programs, MP 3  files, and CD players to name a few. Other combinations of input devices may also be used. Note that the signal generator  204 , decision module  202 , encoders  206 , reference memories  210 , decoders  208 , and sending module  212  may be implemented as hardware or software, which is stored on a computer-readable medium such as a disk, and executed by a processor. 
     In a preferred embodiment, the signal generator  204  receives an input from the various input devices  203 . The signal generator  204  converts the input into data packets. Each data packet may contain video, audio, graphics, alphanumeric or some other form of data. As the signal generator  204  receives a video signal from the camera, for example, it breaks the signal as down into a series of images. The signal generator  204  converts these images into one or more video packets with headers that include the destination addresses for those packets. It is understood that the signal may also be sent in a form other than packetized data. For instance, any multiplexing format may be used including frequency division, time division, code division, spread spectrums, and wavelength division. In a preferred embodiment, the signal generator  204  similarly translates the audio signal into packetized data for transmission across the network  102 . In another embodiment, the sender may function without a signal generator  204 . In this case, the input devices will send audio and video signals directly to the encoders  206 , and the decision module  202  is configured to directly control the encoders  206 . This embodiment is not shown in FIG.  2 . 
     The decision module  202  determines whether the sender  200  will send audio and/or video signals to any receiving client  104  via network  104 . The decision module  202  makes this determination based on any number of local or external factors. The local factors are based on information received from the input devices  203  and may include, by way of example, the volume of the local audio signal, a timer, or manual input from a local user. The decision module  202  may be programmed to decide to send video and audio signals only if the volume of the local audio signal is above a certain threshold. The decision module  202  may also decide to send video at given time intervals based on an internal timer or clock. The decision module  202  may be programmed such that the local user has control over the viewing of video. For instance, input from a local user may include the pressing of a virtual or physical button. By pressing the button, the user may choose to view one or more particular participants in the videoconference or may choose to send local video and audio signals to one or more other participants. 
     External factors are based on information received from various receivers  300  or from the network  102  and may include, by way of example, the volume of received audio signals, command signals received from remote users, or the status of the overall network. The decision module  202  may decide to send video and audio signals if all received audio signals are below a certain threshold. Similarly, the decision module  202  may decide not to send video signals if one or more received audio signals is above a certain threshold. Like the input from the local user, the remote user may choose, by pressing a virtual or physical button, to view a certain conference participant. In this instance, a command from such remote user&#39;s client is sent across the network  102  and received at the local client. Upon receiving such a command, the local client sends the current video and audio signals from the local client across the network to the remote user. The decision module  202  may also monitor the status of the overall network and decide not to send audio and/or video signals or to send signals at reduced data rate if, for instance, the network is too congested. 
     The decision module  202  may also use a combination of both internal and external factors in deciding whether to send audio and video signals. For instance, the decision module  202  may decide to send video and audio signals if the volume of the local audio signal is greater than the volume of every received audio signal and may otherwise decide to send only audio signals. The decision module  202  may be programmed to send audio and/or video signals based upon any one or more of the local and external factors discussed above, or any combination of one or more other factors. Furthermore, the external factors may also include information received from a centralized unit. For example, a centralized unit may compare the volumes of the audio signals for all clients participating in the videoconference and send to each client the address of the loudest one or more clients. The decision module  202  in the clients  104  may then use this information to determine whether to generate and send audio and/or video signals. 
     The encoder  206  encodes each signal before it leaves the sender  200 . Since the signal is, preferably, encoded at the sender and sent to the receiver without any intermediate encoding or mixing at an MCU, the videoconferencing system avoids both tandem and multisource encoding. When the signal has been sent, the decoder  208  at the sending client terminal substantially simultaneously decodes the signal, and the signal is stored in reference memory  210 . A reference memory  210  stores a copy of the last signal sent to each participant in the videoconference. In this manner, the sender is able to keep a record of the images that various receivers are displaying. Based on this reference memory  210 , signals of differing resolutions may be sent to one or more of various receivers  300  that may be participating in the videoconference. With the use of the reference memory  210 , a higher quality image may be sent because only the changes in the image are included in the sent signal. In some cases, the reference memory  210  is not used, for instance, when the first frame of a video image is sent in a given videoconference, if a new participant enters the videoconference, if there is an error in transmission, or at a predetermined time interval. In these cases, a signal representing the entire audio and video image may be sent, possibly with a lower quality resolution. Each individual instantiation of the encoder  206  along with its associated decoder  208  and reference memory  210  operates as is well known in the art. In one embodiment of the present invention, the multiple instantiations of encoders  206  and associated decoders  208  utilize a common set of instructions as is known in the art of computer programming. In one embodiment, identical information is sent to all receivers  300  by sender  200 , and only a single reference memory  210  is maintained in sender  200 . In another embodiment, the reference memories  210  for some receivers  300  are grouped in the sender  200 , and that group of receivers  300  receives identical information from the sender  200 . 
     FIG. 3 is a block diagram of one embodiment of a receiver  300 . The receiver  300  includes output devices  302 , a receiving module  304 , one or more decoders  306 , and one or more reference memories  308 . The receiving module  304  is connected to each of the one or more decoders  306 . Each decoder  306  is connected to a reference memory  308  such that each decoder-reference memory pair decodes and stores, respectively, signals from a different sender  200 . The reference memories  308  are each connected to the output devices  302 . The receiver  300  is the portion of the client  104  that is responsible for receiving audio and video signals from other participants in the videoconference. The output devices  302  present the signals to the user. In a preferred embodiment, the output devices  302  include at least one video display and audio speaker. The video display may display multiple video images in a possibly overlapping window format such that more than one participant in the videoconference may be simultaneously viewed on the video display. 
     The receiving module  304  receives the incoming encoded signals from one or more senders  200 . Each decoder  306  decodes the signals received from a participant. If the receiver  300  is receiving signals from more than one participant, then the receiver  300  may utilize multiple decoders  306 . These decoders  306  may be separate physical hardware components or may be multiplexed through the use of shared software instructions as is known in the art of computer programming. The decoders  306  are each connected to a reference memory  308  or an allocated portion of a larger memory. For example, assume a first sender  200  sends a signal to the receiver  300 . This signal is received by the receiving module  304 , decoded by the decoder  306  and stored in the reference memory  308  reserved for the first sender  200 . The signal from a second sender  200  may be received, decoded by a second decoder  306  and stored in a second memory  308  reserved for the second sender. 
     FIG. 4 is a flow diagram of a preferred embodiment of the cyclic portion of a sending process. One-time initialization and termination processes are omitted for the sake of clarity. In step  402 , the sending terminal  200  receives certain internal and/or external information relevant to the decision process. This information may be based upon local and/or external factors as discussed above. The decision information may be, for example, a volume indicator or a flag that indicates whether a local or external button is pressed. Based on this information, a preferred embodiment decides  406  whether to send audio signals. For instance, the decision module  202  may be programmed to send audio signals if the local volume indicator in the decision information is above all received volumes or if the decision information indicates that a particular button has been pressed or released. 
     In step  406 , if the decision module  202  determines that the sender  200  is not going to send audio, then the sender  200 , in step  417 , determines whether to send video. If the decision module  202  determines that the sender  200  is going to send audio, then, in step  408 , the signal generator  204  generates an audio packet. Note that the audio packet is generated only when the sender  200  will be sending an audio signal. By not generating any unsent signals, the sender  200  eliminates the unnecessary use of resources such as the resources required to remove loud speaker echoes from the microphone signal. The audio packet is then encoded  410 , sent  412 , and decoded  414 . The reference memory  210  for the audio signal is then updated  416 . The decision module  202  then determines whether to send a video signal. 
     If the decision module  202  determines, in step  417 , that the sender  200  will send video signals, then the signal generator  204  generates  418  such signals. Note that the video signals are generated only when they will be transmitted, thus eliminating unnecessary use of resources in the generating of unsent signals. Once the video signals are generated, the encoder  206  encodes  420  the signals, and the sender  200  sends  422  the signals to the receiver  300 . The decoder  208 , located in the sender  200 , decodes  424  a copy of the signals that were sent to the receiver  300 . The sender updates  426  the reference memory  210  for the video signal with the last decoded video signal sent to the receiver. The sender  200  then returns to step  402  to repeat the process of determining whether to send another video signal, or the same video signal to another receiver  300  via network  102 . 
     Note that the decision module  202  determines both whether to send audio signals and whether to send video signals. The decision module  202  may decide to send only audio signals, only video signals or both audio and video signals. 
     FIG. 5 is a flow diagram of a preferred embodiment of a receiving process. The receiver  300  receives  502  an encoded video packet from some sender  200 . The receiver then decodes  504  the video packet. The receiver  300  may similarly receive and decode audio signals. Note that the signals may be received directly from the sender  200  via network  102  and decoded without any intermediate encoding and decoding, thus preserving high signal quality and reducing delay and delay fluctuations. The receiver then updates  506  its reference memory  308  for the sender  200  that sent the packet. This receiver reference memory  308  contains virtually identical data to the reference memory  210  at the sender  200 . As a result, if the sender  200  sends signals indicative only of changes since the last transmission, the receiver  300  may use these changes to update the last received signal that is stored in memory  308 . The receiver then displays  508  the updated video image and plays the audio associated with the most recent transmission. The video images may be displayed in any number of ways including displaying individual windows for each sender, with one or more images displayed at a time. Audio signals may similarly be presented in any number of ways, including mixing the signals such that all senders are heard simultaneously, or presenting only the loudest signal. The determination of how such received signals are presented to the user of the receiver may be made by one or more various decision algorithms stored in a local processor (not shown) forming part of the receiver or under manual control of the user. 
     It will be apparent to those skilled in the relevant field that, in certain preferred embodiments, the subject invention may be used to wholly (or partially) eliminate the need for a complex and expensive MCU. In accordance with certain embodiments described herein, the MCU may be wholly eliminated, thus greatly reducing the cost and complexity of a videoconferencing facility. 
     The foregoing description is offered for illustrative purposes only. Numerous modifications and variations will be apparent to those skilled in the art based upon the foregoing discussion, while still falling within the spirit and scope of the invention claimed below and its equivalents.