PATENT DOCUMENT

Publication Number: US-8249237-B2
Application Number: US-201113099331-A
Country: US
Kind Code: B2

Title: Heterogeneous video conferencing

Abstract:
Some embodiments provide an architecture for establishing a multi-participant conference. This architecture has one participant&#39;s computer in the conference act as a central content distributor for the conference. The central distributor receives data (e.g., video and/or audio streams) from the computer of each other participant, and distributes the received data to the computers of all participants. In some embodiments, the central distributor receives A/V data from the computers of the other participants. From such received data, the central distributor of some embodiments generates composite data (e.g., composite image data and/or composite audio data) that the central distributor distributes back to the participants. The central distributor in some embodiments can implement a heterogeneous audio/video conference. In such a conference, different participants can participate in the conference differently. For instance, different participants might use different audio or video codecs. Moreover, in some embodiments, one participant might participate in only the audio aspect of the conference, while another participant might participate in both audio and video aspects of the conference.

Claims:
1. A non-transitory computer readable medium storing a computer program for execution by at least one processor of a central distributor device participating in a conference, the computer program comprising sets of instructions for:
 receiving conference content data from (i) a first non-central distributor device according to a first set of conference parameters and (ii) a second non-central distributor device according to a second, different set of conference parameters, the first and second non-central distributor devices participating in the conference; 
 generating composite conference content data using (i) the received conference content data and (ii) conference content data captured locally at the central distributor device; and 
 distributing the composite conference content data to (i) the first non-central distributor device according to the first set of conference parameters and (ii) the second non-central distributor device according to the second set of conference parameters. 
 
     
     
       2. The non-transitory computer readable medium of  claim 1 , wherein the conference content data from the first non-central distributor device comprises video data and audio data while the conference content data from the second non-central distributor device comprises only audio data. 
     
     
       3. The non-transitory computer readable medium of  claim 2 , wherein the set of instructions for receiving conference content data comprises sets of instructions for:
 defining a video-decoding pipeline for the conference content data from the first non-central distributor device; 
 defining an audio-decoding pipeline for the conference content data from the first non-central distributor device; and 
 defining an audio-decoding pipeline for the conference content data from the second non-central distributor device. 
 
     
     
       4. The non-transitory computer readable medium of  claim 3 , wherein no video-decoding pipeline is generated for the conference content data from the second non-central distributor device. 
     
     
       5. The non-transitory computer readable medium of  claim 1 , wherein the conference content data from the first non-central distributor device comprises video images having a first resolution and the conference content data from the second non-central distributor device comprises video images having a second, different resolution. 
     
     
       6. The non-transitory computer readable medium of  claim 5 , wherein the set of instructions for generating the composite conference content data comprises sets of instructions for:
 resizing the video images from the first non-central distributor device from the first resolution to a composite buffer size; and 
 resizing the video images from the second non-central distributor device from the second resolution to the composite buffer size. 
 
     
     
       7. The non-transitory computer readable medium of  claim 6 , wherein the set of instructions for generating the composite conference content data further comprises a set of instructions for generating composite video images using the resized video images. 
     
     
       8. The non-transitory computer readable medium of  claim 1 , wherein the conference content data from the first non-central distributor device comprises video images encoded in a first format and the conference content data from the second non-central distributor device comprises video images encoded in a second format. 
     
     
       9. The non-transitory computer readable medium of  claim 8 , wherein the first format is H.263 and the second format is H.264. 
     
     
       10. The non-transitory computer readable medium of  claim 8 , wherein the set of instructions for receiving the composite conference content data comprises sets of instructions for:
 decoding the video images from the first non-central distributor device using a first decoder; and 
 decoding the video images from the second non-central distributor device using a second decoder. 
 
     
     
       11. A method for providing a conferencing application for a device that participates in a conference as a central distributor of the conference, the method comprising:
 providing a local content capture module for capturing conference content at the device; 
 providing a set of receiver modules for receiving, at the device, conference content from a plurality of non-central distributor devices, wherein at least two of the non-central distributor devices transmit conference content to the device according to different conference parameters; 
 providing a compositing module for producing composite conference content data comprising data captured by the local content capture module and data received by at least one of the receiver modules; and 
 providing an output module for distributing the composite conference content data to the plurality of non-central distributor devices. 
 
     
     
       12. The method of  claim 11 , wherein the set of receiver modules comprises a set of decoders for decoding video images from the non-central distributor devices, the set of decoders comprising at least two different decoders for decoding video images in different formats. 
     
     
       13. The method of  claim 11 , wherein the set of receiver modules comprises a set of resizers for resizing video images from the non-central distributor devices to a standard size, the set of decoders comprising at least two different resizers for resizing video images having different resolutions. 
     
     
       14. The method of  claim 11 , wherein the compositing module comprises:
 a compositing buffer for storing video images from the non-central distributor devices and the local conference capture module; and 
 an encoder for encoding a composite video image from the video images stored in the compositing buffer. 
 
     
     
       15. The method of  claim 14 , wherein the output module comprises a redundancy remover for removing a particular video image from the composite video image when distributing the composite video image to a non-central distributor device from which the device received the particular video image. 
     
     
       16. The method of  claim 11 , wherein the local content capture module comprises a module for receiving images from a camera at the device. 
     
     
       17. The method of  claim 11 , wherein the local content capture module comprises a module for receiving audio from a microphone at the device. 
     
     
       18. A conference system comprising:
 a first non-central distributor device for transmitting conference content data according to a first set of conference parameters; 
 a second non-central distributor device for transmitting conference content data according to a second set of conference parameters; and 
 a central distributor device for (i) receiving the transmitted conference content data from the first and second non-central distributor device, (ii) generating composite conference content data from the received conference content data and additional conference content data captured locally at the central distributor device, (iii) transmitting the generated composite conference content data to the first and second non-central distributor devices, and (iv) outputting the generated composite conference content data locally at the central distributor device. 
 
     
     
       19. The system of  claim 18 , wherein outputting the generated composite conference content data locally comprises displaying a composite video image generated using images received from the first and second non-central distributor devices and locally captured by a camera at the central distributor device. 
     
     
       20. The system of  claim 18  further comprising at least one additional non-central distributor device for transmitting conference content according to a third set of conference parameters.

Description:
CLAIM OF BENEFIT TO PRIOR APPLICATION 
     This Application is a continuation application of U.S. patent application Ser. No. 11/118,297, filed Apr. 28, 2005, now issued as U.S. Pat. No. 7,949,117. U.S. Pat. No. 7,949,117 is incorporated herein by reference. 
    
    
     BACKGROUND 
     In recent years, users of local and wide area networks (e.g., the Internet) have upgraded to increasingly higher bandwidth connections. The common user also has access to greater computer hardware processing power. At the same time, the coders and decoders (codecs) for video transmission over a network connection have seen improvements such that an individual user has the capability to stream and receive real-time video over the Internet with off-the-shelf components. All this has allowed individual users to begin chatting, sharing, and videoconferencing with point-to-point technologies on their computers. 
     However, bandwidth remains a constrained resource that must be shared over many users. Likewise, processing power is typically shared by the operating system and several applications in a typical user&#39;s computer hardware. These factors have been barriers to the use of personal computers in establishing a conference with more than two participants. Such a conference will be referenced below as a multi-participant conference. 
     Several approaches are possible for multi-participant conferencing. One such approach is the full-mesh topology, which is the extension of two-participant point-to-point methods to multi-participant conferencing. Under the full-mesh topology, each participant sends all of its audio and/or video (A/V) data to all other participants in the multi-participant conference. However, the full mesh topology requires a high amount of processing power and broad bandwidth at and between each participant of the multi-participant conference. Even with just a few participants, the full-mesh topology quickly becomes untenable because each participant and each network connection is responsible for sending and receiving a burdensome amount of data. Moreover, the weakest connection or hardware point determines the maximum capability of a conference for all participants in the full-mesh topology. 
     The star topology is another possible approach for multi-participant conferencing. In prior art this approach uses a central server to receive data from all participants in the conference and send all that data back out to each participant. The required server needs high bandwidth and processing power. The server requirements scale with the number of conferences to be hosted, making this approach unusable for wide scale deployment. 
     Thus, there is a need in the art for a better architecture for multi-participant conferencing. Ideally, such an architecture would allow the participants to use off-the-shelf computers and typically available bandwidth and not require the deployment of dedicated servers. 
     SUMMARY OF THE INVENTION 
     Some embodiments provide an architecture for establishing a multi-participant conference. This architecture has one participant&#39;s computer in the conference act as a central content distributor for the conference. The central distributor receives data (e.g., video and/or audio streams) from the computer of each other participant, and distributes the received data to the computers of all participants. 
     In some embodiments, the central distributor receives A/V data from the computers of the other participants. From such received data, the central distributor of some embodiments generates composite data (e.g., composite image data and/or composite audio data) that the central distributor distributes back to the participants. 
     The central distributor in some embodiments can implement a heterogeneous audio/video conference. In such a conference, different participants can participate in the conference differently. For instance, different participants might use different audio or video codecs. Moreover, in some embodiments, one participant might participate in only the audio aspect of the conference, while another participant might participate in both audio and video aspects of the conference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the invention are set forth in the appended claims. However, for purpose of explanation, several embodiments of the invention are set forth in the following figures. 
         FIG. 1  illustrates a multi-participant focus-point conference. 
         FIG. 2  illustrates a focus point assessment process according to some embodiments of the invention. 
         FIG. 3  illustrates participants performing static bandwidth estimation with a remote server. 
         FIG. 4  illustrates a first computer inviting a second computer to establish a two-participant conference. 
         FIG. 5  illustrates a first computer inviting a third computer to establish a multi-participant conference. 
         FIG. 6  illustrates a detailed process flow of acceptance by a participant. 
         FIG. 7  illustrates a process flow for a focus computer that receives data from a participant after acceptance by the participant. 
         FIG. 8  illustrates an in-call bandwidth adjustment process. 
         FIG. 9  illustrates a focus computer detecting loss from one non-focus computer. 
         FIG. 10  illustrates a non-focus computer detecting loss from the focus computer. 
         FIG. 11  illustrates a focus computer detecting loss from multiple non-focus computers. 
         FIG. 12  illustrates multiple non-focus computers detecting loss from a focus computer. 
         FIG. 13  illustrates a focus computer distributing its upload bandwidth over two participants. 
         FIG. 14  illustrates a focus computer distributing its upload bandwidth over three participants. 
         FIG. 15  illustrates an example of a video conference. 
         FIG. 16  illustrates an example of data exchange in a four participant conference. 
         FIG. 17  illustrates the video codec section of the focus point module or a focus computer. 
         FIG. 18  illustrates a non focus video codec section of a non focus point module of a non focus computer. 
         FIG. 19  illustrates an audio codec section of the focus point module of the focus computer. 
         FIG. 20  illustrates a non focus audio codec section of a non focus point module of a non focus computer. 
         FIG. 21  illustrates an example where a participant does not provide any video data to a focus computer. 
         FIG. 22  illustrates an example of a focus point video codec. 
         FIG. 23  illustrates an example where a participant does not provide any audio or video data to a focus computer. 
         FIG. 24  illustrates an example of a focus point audio codec. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, numerous details are set forth for purpose of explanation. However, one of ordinary skill in the art will realize that the invention may be practiced without the use of these specific details. In other instances, well-known structures and devices are shown in block diagram form in order not to obscure the description of the invention with unnecessary detail. 
     Some embodiments provide an architecture for establishing a multi-participant conference. This architecture has one participant&#39;s computer in the conference act as a central content distributor for the conference. In some embodiments, the central distributor is a participant that meets certain criteria. The criteria of some embodiments may include whether the participant has sufficient bandwidth and processing power. The central distributor is also referred to below as a focus point computer or focus computer for the multi-participant video conference. The computers of the other participants will be referred to below as non-focus computers. 
     The central distributor receives data (e.g., video and/or audio streams) from the computer of each other participant, and distributes the received data to the computers of all participants. In some embodiments, the central distributor (1) receives A/V data from the computers of the other participants, and from such data, (2) generates composite data (e.g., composite image data and/or composite audio data) that it distributes back to the participants. 
     The central distributor in some embodiments can implement ,a heterogeneous audio/video conference. In such a conference, different participants can participate in the conference differently. For instance, different participants might use different audio or video codecs. Moreover, in some embodiments, one participant might participate in only the audio aspect of the conference, while another participant might participate in both audio and video aspects of the conference. 
     I. Focus Point Architecture 
       FIG. 1  illustrates an example of a conference architecture  100  of some embodiments of the invention. This architecture allows multiple participants to engage in a conference. In the example illustrated in  FIG. 1 , four participants A, B, C, and D are engaged in a conference through their four computers  105 - 120 . 
     The architecture  100  has participant D&#39;s computer  105  serve as a focus point computer and the computers  110 ,  115 , and  120  of the other participants A, B, and C serve as non-focus computers. During the conference, each non-focus computer  110 ,  115 , and  120  connects to the focus point  105  through a network (not shown). The network can be any network, such as a local area network, a wide area network, a network of networks (i.e., the Internet), etc. The network allows conference data to pass between the focus computer  105  and the non-focus computers  110 ,  115 , and  120 . As shown  FIG. 1 , the non-focus computers  110 ,  115 , and  120  do not pass conference data directly to each other in the focus-point architecture  100 . 
     During the conference, the focus point computer  105  serves as the central distributor of audio/video content to the other computers. As the central distributor of audio/video content, the focus computer  105  receives A/V data from each participant, composites and encodes the received data, and then transmits the composite data to each of the non-focus computers. 
     In some embodiments, the focus point computer removes a particular non-focus participant&#39;s data from the composite data that the focus point computer transmits to the particular non-focus participant. Also, in some embodiments, the focus point computer embeds relative audio strength values in the composite audio data to facilitate the use of audio level meters and audio panning at the non-focus computers. Such audio and video compositing are further described in U.S. Pat. No. 7,864,209 Application entitled “Audio Processing in a Multi-Participant Conference”, and in U.S. Pat. No. 7,817,180 entitled “Video Processing in a Multi-Participant Video Conference”. Both these patents are incorporated herein by reference. 
     Some embodiments are implemented by an A/V conference application (e.g., iChat® provided by Apple Computer, Inc.) that allows a computer to act as a focus computer or a non-focus computer in a multi participant conference. As such, during an A/V conference, the conferencing application receives, composites, and distributes A/V content when serving as a focus computer. However, one of ordinary skill will realize that other embodiments may implement the receiving, compositing, and distribution as one or more separate modules. 
     In some embodiments, a focus point computer sets up a multi-participant conference by inviting two or more participants to join the conference. Before a computer can act as a focus point computer that is capable of inviting multiple participants to a multi-participant conference, the computer must first be designated as a focus point capable computer. The next section (Section II) describes how some embodiments designate a computer as focus point capable. Section II also describes how a focus point computer invites participants to set up a multi-participant conference. Section III describes messaging over Session Initiation Protocol and encryption. Section IV describes the operations of focus and non-focus computers once a multi-participant conference is underway. Section V describes heterogeneous multi-participant conferencing. 
     II. Setting Up a Conference 
     A. Focus-Point Assessment Process 
     As mentioned above, some embodiments are implemented by an A/V conferencing application that allows a computer to act as a focus or non-focus computer in a multi participant conference. When the conferencing application of some embodiments starts on a particular computer, the application performs a focus-point assessment process to determine whether the particular computer can serve as a focus point for a multi-participant conference. 
       FIG. 2  illustrates an example of such a focus-point assessment process  200  of some embodiments. As shown in this figure, this process  200  starts (at  205 ) each time that the conferencing application starts. Next, at  210  the process performs an inspection of the participant&#39;s computer. To aid in the determination of whether a computer can be a focus point, and to provide additional constraints in the default static conference capabilities of a computer, some embodiments perform a local hardware inspection at  210  of the focus-point assessment process  200 . If, at  210 , the local hardware determination does not meet the criteria for a focus point, then the focus-point assessment process  200  transitions to  215  where the computer is designated as non-focus point capable. 
     If the hardware determination does meet the criteria for a focus point, then the focus point assessment process  200  proceeds to  216  where the process begins a determination of whether the computer has sufficient bandwidth to act as a focus point computer. At  216 , some embodiments first determine whether a static bandwidth test is required. In these embodiments, the results of prior static bandwidth tests are stored to non-volatile memory (i.e., cached). These embodiments check whether the cached bandwidth values are still valid. If the cached bandwidth values are still valid, the process  200  forgoes the static bandwidth test described below (at  218 ) and instead uses the cached values to determine whether the bandwidth criteria for a focus computer is met (at  220 ). The cached values of these embodiments also determine the default conferencing capabilities of the computer. 
     If, at  216 , the cached values are no longer valid, then the focus-point assessment process performs a new or initial static bandwidth test (at  218 ) to determine whether the conferencing application&#39;s computer meets the bandwidth criteria for acting as a focus point. As further described below, the results of this initial test are cached in some embodiments and used to set the default conferencing capabilities of the computer. 
     To perform the initial static bandwidth test at  218 , some embodiments employ a server (e.g., the “.mac”® server provided by Apple Computer, Inc.) that is located at a remote location from the conferencing application&#39;s computer.  FIG. 3  illustrates a conferencing application&#39;s computer  305  performing an initial static bandwidth test with a remote bandwidth server  310  through a network  315  (e.g., through the Internet). As shown in this figure, the initial static bandwidth test involves the computer  305  sending a request to the server  310  for an assessment of the network bandwidth available to the computer  305 . In response, the server  310  sends and receives packets from the computer  305  to assess its available bandwidth. Once the server  310  has completed its assessment of the computer&#39;s available bandwidth, it provides the computer with an estimate of its bandwidth, as shown in  FIG. 3 . As further shown in  FIG. 3 , the bandwidth server  310  receives bandwidth determination requests from other computers. 
     Due to the number of requests at a given time, or for a variety of other reasons (e.g., network congestion, downtime, etc.), the bandwidth server  310  may not be available to respond to a particular request by the focus-point assessment process  200 . For the cases when the bandwidth server is unavailable, the conferencing application of some embodiments caches (i.e., retains in non-volatile memory) the last successful static bandwidth estimate. 
     Regardless of whether the bandwidth estimate is newly performed ( 218 ) or is cached ( 216 ), the focus-point assessment process  200  then applies (at  220 ) the bandwidth estimate to a set of rules that determine whether the computer can be a focus point. If the initial static bandwidth estimate does not meet (at  220 ) the criteria for a focus point, then the process  200  transitions to  215 . At  215 , the computer is designated as non-focus point capable and then the focus-point assessment process  200  terminates. If the initial static bandwidth estimate is deemed sufficient (at  220 ) to meet the focus point bandwidth criteria, the process  200  transitions to  225  and the participant is designated as focus point capable. A focus capable computer may act as either a focus computer or a non-focus computer, and may host or join both peer-to-peer and multi-participant conferences. A non-focus computer, however, may host only a peer-to-peer conference, but may join both peer-to-peer and multi-participant conferences. 
     At  230 , the focus-point assessment process  200  applies the initial bandwidth estimate to a set of rules to define the default conferencing capability (i.e., defines a set of default conference parameters) for the computer to potentially use in the next conference the computer initiates or joins. For instance, some embodiments utilize sets of rules for the cases where the computer is (1) a participant in a peer-to-peer conference, (2) a client (i.e., a non-focus computer) in a multi-participant conference, or (3) a focus point in a multi-participant conference. Tables 1-3 below illustrate examples of such rules for some embodiments. These tables illustrate examples where the initial estimated bandwidth determines the default frame rate and frame size for the focus point and non-focus point computers&#39; encoders. These tables also show that the rules vary depending upon whether the participant acts as a focus point or a client, and whether the conference is peer-to-peer or multi-participant. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Either Participant in Peer-to-Peer Conference 
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 frame size 
               
               
                   
                 bandwidth (bps) 
                 frame rate 
                 (H.263/H.264) 
               
               
                   
                   
               
               
                   
                  &gt;1.0M 
                 30 fps 
                 352 × 288/640 × 480 
               
               
                   
                 500K-1.0M 
                 30 fps 
                 352 × 288/320 × 240 
               
               
                   
                 &lt;500K 
                 15 fps 
                 176 × 144/160 × 120 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Client (Non-Focus Computer) in Multi-Participant Conference 
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 frame size 
               
               
                   
                 bandwidth (bps) 
                 frame rate 
                 (H.263/H.264) 
               
               
                   
                   
               
               
                   
                 &gt;500K 
                 30 fps 
                 352 × 288/320 × 240 
               
               
                   
                 &lt;500K 
                 15 fps 
                 176 × 144/160 × 120 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Focus Point Computer in Multi-Participant Conference 
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 frame size 
               
               
                   
                 bandwidth (bps) 
                 frame rate 
                 (H.264) 
               
               
                   
                   
               
               
                   
                 &gt;500K 
                 30 fps 
                 320 × 240 
               
               
                   
                 200K-500K 
                 15 fps 
                 160 × 120 
               
               
                   
                 &lt;200K 
                 15 fps 
                  80 × 60 
               
               
                   
                   
               
            
           
         
       
     
     At  230 , the focus-point assessment process  200  of some embodiments sets the computer&#39;s default conference capabilities not only based on the bandwidth estimate but also on the hardware inspection described above. Table 4 below illustrates one possible set of these rules that are based on both hardware and bandwidth considerations. As shown in this table, the hardware configurations can include type, speed, and number of processors, where the processors in this example are the G-series processors used by Apple Computer, Inc. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Maximum Conferencing/Encoding Capability by Processor 
               
            
           
           
               
               
               
               
            
               
                   
                 #, type processor(s) 
                   
                 frame size 
               
               
                   
                 speed (in GHz) 
                 frame rate 
                 (H.263/H.264) 
               
               
                   
                   
               
               
                   
                 2, G5 (2.5+) 
                 30 fps 
                 352 × 288/640 × 480 
               
               
                   
                 1, G4 (0.933-1.33) 
                 15 fps 
                 352 × 288/160 × 120 
               
               
                   
                 1, G3 (0.600-0.867) 
                 15 fps 
                 176 × 144/na 
               
               
                   
                   
               
            
           
         
       
     
     Some embodiments may store the information gathered by the focus-point assessment process  200  for later use. For instance, this stored information may be used later if the conferencing application cannot establish contact with the bandwidth determining server. This information may also be transmitted to a participant as part of a call or invitation to conference. The invitation to begin a conference is described next. 
     B. Setting Up a Multi-Participant Conference 
     Once a computer is deemed focus point capable, the computer may initiate a two-participant conference with another computer. The focus point capable computer may further invite additional non-focus computers to establish a multi-participant conference.  FIGS. 4-6  illustrate one example of such a multi-participant conference set up. 
     Specifically,  FIG. 4  illustrates a process  400  that first focus-capable computer  405  of some embodiments performs to invite a second computer  415  to join a conference. The focus capable computer  405  may then invite additional non-focus computers  440  and  445  to join the conference in-progress, in order to establish a multi-participant conference. For purposes of nomenclature, the focus capable computer will be referred to as a focus computer when a third (non-focus) computer joins the existing two-participant conference and a multi-participant conference is established. 
     1. Invitation and Acceptance 
     In the examples illustrated in  FIGS. 4-6 , it is assumed that the first computer  405  has been designated focus point capable by a focus-point assessment process  200  that was performed previously. To initiate a new conference, the first focus-capable computer  405  sends an invitation  410  to a second computer  415 . In some embodiments, the invitation  410  typically includes the maximum conference capabilities of the first focus-capable computer  405 . These capabilities are part of the set of default conference parameters (e.g., frame rate and size, codec, static bandwidth and hardware configuration) that were defined for the computer  405  in the previously performed assessment process  200 . Also, in some embodiments, the invitation uses messaging over Session Initiation Protocol (SIP), which will be further described in detail later. 
     In some embodiments, a participant operating the first computer may specify conference parameters that do not utilize the first computer&#39;s full conferencing capabilities (e.g., selecting an audio conference even though the first computer  405  might have sufficient resources for a high definition video conference). Hence, in such cases, the invitation  410  does not include the maximum conference capabilities of the first focus-capable computer  105 . 
     Upon receiving the invitation, the second computer  415  may decline or accept. The second computer  415  may decline by sending a message to decline to conference. The second computer  415  may also accept by sending an acceptance message  420  back to the first focus-capable computer  405 . The acceptance message of some embodiments may include a subscription message. The subscription message informs the first focus-capable computer  405  that the second computer should receive conference notifications. In some embodiments, the acceptance message includes one or more conferencing parameters that indicate the second computer&#39;s conferencing capabilities in addition to the acceptance of the offer to conference. In some embodiments, the acceptance also uses messaging over Session Initiation Protocol (SIP). 
     If the second computer  415  accepts, then the first focus-capable computer  405  and the second computer  415  perform a dynamic bandwidth determination  425  between their two locations. In some embodiments, the dynamic bandwidth determination may aid in configuring the initial conference settings for the new two-participant conference. For instance, the dynamic bandwidth determination may aid in setting the initial frame rate and size for the encoders of the participants&#39; computers. 
     The dynamic bandwidth determination of some embodiments measures the speed and/or loss rate of the connection between two computers by transmitting and receiving a series of successively larger packet groups. For instance, one embodiment sends three groups of packets from each transmitter to each receiver of the two computers. In this embodiment, the first group contains relatively small packets that are suitable for estimating the bandwidth of slow connections (e.g., less than 100 Kbps). The second group contains larger packets for estimating medium speed connections (e.g., between 100 Kbps and 500 Kbps). The third group contains large packets, which allows accurate bandwidth estimation for higher speed connections (e.g., greater than 500 Kbps). Some embodiments that employ this technique can make accurate estimates in less than one second. The process of dynamic bandwidth determination is described further in U.S. patent application 10/770,181, entitled “Automatic Detection of Channel Bandwidth,” now U.S. Pat. No. 7,653,719 which is incorporated herein by reference. 
     During the dynamic bandwidth determination of some embodiments, one of the participants&#39; computers may downgrade one or more of the computer&#39;s local conferencing parameters based on the actual determined dynamic bandwidth available for the conference. For instance, one computer might be capable of large frame sizes, but the bandwidth of the connection of the other computer may not support large frame sizes. Some embodiments use the tables shown above to adjust the computer&#39;s various local conferencing parameters based on the dynamic bandwidth determination. These adjustments to a computer&#39;s conferencing parameters, in turn adjust the settings for the conference, both at setup and during the conference. 
     In some embodiments, the results of the dynamic bandwidth determination are stored to a log in non-volatile memory. These logged results may be examined to improve the bandwidth estimate by discarding outliers and performing averaging, or to accelerate the connection time of the conference by skipping the dynamic bandwidth detection step. Once dynamic bandwidth determination indicates the initial conference settings (e.g., the initial frame rate and size for the conference) between the participants&#39; computers, the second computer  415  sends an A/V transmission to the first focus-capable computer  405 . 
     Upon receiving the A/V transmission, the first focus-capable computer uses the initial conference settings for the conference. As described above, the initial conference settings form a set of parameters that contain the capabilities of the focus and non focus computers constrained by each participants&#39; selections for the conference, and further constrained by the dynamic bandwidth determination. For instance, the first focus-capable computer of some embodiments uses the set of conference parameters to configure its coding and decoding modules for sending and receiving data to and from the second computer. These configurations might define a decoder for receiving data that was encoded by using a particular audio or video codec. These configurations might also define other means for handling incoming data such as the configuration of a resizer that adjusts the frame sizes, or of a frame rate controller that controls encoding and/or decoding frame rates. Similarly, these parameters may be used in some embodiments to define the properties of an encoder for sending data back out to the particular participant or to all the participants in the conference. 
     The codec components of the focus and non-focus capable computer will be further described in Sections IV and V. Also, as further described below in Section V, the ability of the focus and non-focus computers to dynamically set up their conference parameters based on their capabilities and the available bandwidth, allows the focus computer to establish a heterogeneous multi-participant conference. A heterogeneous conference is one where different conferencing computers participate differently in the conference (e.g., transmit and/or receive different types of data, utilize different A/V encoders, etc.). 
     2. Overview of Switching from a Two-Participant Conference to a Multi-Participant Conference 
     Once a two-participant conference is underway, the first focus-capable computer  405  of some embodiments may invite additional computers, such as computers  440  and  445  in  FIG. 4 . In such a case, the two-participant conference changes to a multi-participant conference. For instance,  FIG. 5  illustrates that the first focus-capable computer  405  may invite a third computer  440  (and a fourth computer  445 ) to the two-participant conference already established with the second computer  415 . 
       FIG. 5  illustrates the invitation  510  and acceptance  520  involving the third computer  440 . In some embodiments, the invitation and acceptance (as well as the invitation and acceptance of the fourth computer  445 ) proceed in the same manner as the invitation and acceptance process that was described above for the second computer  415 . 
     However, in the embodiments described below, the process for inviting and accepting the third and fourth computers  440  and  445  is slightly more involved than the process for inviting and accepting of the second computer  415 . For instance, when the third computer  440  accepts the invitation to join the conference, some embodiments will send a notification to any other subscribed computers, in this case the second computer  415 , that the third computer  440  has joined the conference. 
     More specifically, once the third computer  440  (1) receives an invitation  510 , (2) accepts  520 , and (3) performs dynamic bandwidth determination  525  with the first focus-capable computer  405 , the third computer  440  sends A/V data to the first focus-capable computer  405 . As mentioned above, this A/V data might include a set of conference parameters that indicate the third computer&#39;s maximum capability for the conference. The first focus-capable computer  405  upon receiving the third computer&#39;s A/V data may make certain adjustments for supporting multiple participants in the newly established multi-participant conference. 
     For instance, as further described below, the first focus-capable computer  405  might realize that the addition of the third computer diminishes the available bandwidth between the first and second computers. Accordingly, the first focus-capable computer  405  might then adjust one or more conference settings (e.g., size of the video images transmitted back and forth) to account for this difference. The first focus-capable computer would make such adjustments as participants join or leave the conference in order to maintain the conference quality and reliability. Such adjustments are further described below in sub-sections  3  and  4 . 
     One of ordinary skill will recognize that multiple variations are possible for the setup process illustrated in  FIGS. 4 and 5 . For instance, in the illustrated embodiment, only the focus computer  405  invites additional participants to join the conference. However, in other embodiments, a participant other than the focus computer  405  may invite additional participants to join the conference. 
     Some embodiments may limit the total number of participants to four video participants, or to ten audio participants, to preserve the quality of the conference. However, one of ordinary skill will recognize that many combinations of video and audio participants are possible. In some embodiments, only the available resources limit the permutations of participant combinations. As mentioned above, these resources might include the bandwidth and local hardware available to the conference participants of these embodiments. 
     3. Participant Computer After Acceptance 
       FIG. 6  illustrates a process  600  that a non-focus computer performs when it receives an invitation to join a conference from a focus computer. As shown in this figure, this process starts (at  605 ) when the non-focus computer receives an invitation from the focus computer. At  610 , the non-focus computer&#39;s participant decides whether to accept the invitation to conference. If the non-focus computer&#39;s participant decides to decline the conference, the non-focus process  600  sends (at  615 ) a message to the focus computer declining the conference. After  615 , the process  600  ends. 
     On the other hand, when the non-focus computer&#39;s participant decides to accept the invitation, the non-focus process  600  transitions from  610  to  620 , where the non focus computer sends an acceptance to the focus computer. In some embodiments, the acceptance of the invitation includes the initial conference parameters (e.g., the codec, frame rate and size information) that indicate the static conferencing capabilities of the non-focus computer. Upon receiving this data, the focus computer of some embodiments defines the initial conference settings for its conference communications with the non-focus computer. Also at  620 , the non-focus computer sends a subscription message to the focus computer. The subscription message triggers the focus and non-focus computers to begin (at  625 ) a dynamic bandwidth determination. As described above, this dynamic bandwidth determination identifies an estimated bandwidth between the focus and non-focus computers. 
     After the dynamic bandwidth determination at  625 , the non-focus process  600  specifies (at  630 ) the initial conference settings (e.g., the codec, frame rate and size, etc.) that the non-focus computer should use in this conference. In some embodiments, the process specifies these settings (at  630 ) based on (1) the non-focus computer&#39;s default conference parameters, (2) the estimated bandwidth (identified at  630 ) between the focus and non-focus computers, and (3) any conference parameter specified in the focus computer&#39;s invitation. 
     The non-focus computer&#39;s default conference parameters are the conference parameters that the non-focus computer&#39;s video conferencing application specifies after this application performs its focus-point assessment process  200 . The non-focus computer might not be able to use its default conference parameters when the focus computer invites the non-focus computer to a conference. For instance, the dynamic bandwidth determination (which is performed at  625   630 ) might specify an estimated bandwidth that might not be able to sustain some of the default parameters (e.g., frame sizes or codecs). Also, the focus computer&#39;s invitation might specify one or more conference parameters that are lower on the hierarchy of parameters. For instance, the non-focus computer&#39;s default conference parameters include the use of an H.264 encoder, but the focus computer&#39;s only invites the non-focus computer to use an H.263 encoder. 
     Accordingly, at  630 , the process defines the initial conference parameters by starting with the non-focus computer&#39;s default conference parameters, and then possibly degrading one or more of these parameters to meet the parameters specified by the focus computer, or to meet the dynamically estimated bandwidth. When downgrading the parameters based on the dynamically estimated bandwidth, the process  600  traverses down the hierarchy of conference parameter sets in its conference parameter tables, which were described above. In some embodiments, downgrading the conference parameters might include, e.g., switching to a lower bit rate codec, reducing the frame rate and/or the frame size of the non-focus computer&#39;s encoder. 
     After  630 , the process  600  defines the non-focus computers&#39; A/V codecs (i.e., its one or more encoders and decoders) based on the initial conference parameters defined at  630 . Next, at  640 , the process  600  sends the non-focus computer&#39;s A/V data to the focus computer. After  640 , the process  600  performs an in-call adjustment process, which might result in the modification of the conference parameters that the focus and non-focus computers use in the conference to communicate with each other. The in-call adjustment process will be described in the next sub-section. After performing the in-call adjustment process, the process  600  ends. 
     4. In-Call Adjustments due to Actual Available Bandwidth and Loss/Delay 
     When participants join or leave a multi-participant conference, some embodiments allow for in-call adjustments to the conference parameters of one or more computers of one or more participants.  FIG. 7  conceptually illustrates a process  700  that the focus point computer iteratively performs during a multi-participant conference. This process  700  allows the focus computer to initiate in-call adjustments when a participant leaves or joins the conference. 
     As shown in  FIG. 7 , the focus computer receives (at  705 ) A/V data from the participants during the conference. Next, at  715 , the process  700  of the focus computer determines whether any participant has left the conference. If so, the focus computer sends (at  720 ) a notification of the participant&#39;s departure to the other participants in the conference. The non-focus computers of these other participants then use this data to deallocate the resources that they had previously allocated for decoding and displaying the departing participant&#39;s data. 
     At  720 , the process  700  also initiates an in-call adjustment operation. This in-call adjustment operation can result in an upgrade of the conference parameters for one or more of the participants. For instance, the departure of a participant frees up more bandwidth for the focus computer to share with the remaining non-focus computers. This increase in bandwidth might in turn allow one or more of the computers to change to bigger frame sizes or better encoders. The computers might also change to bigger frame sizes or better encoders if the departing non-focus computer&#39;s capabilities and/or bandwidth previously required the focus point computer to utilize the smaller frame sizes or the weaker encoders. After a participant leaves, the focus and non-focus computers of some embodiments go through an adjustment period to detect losses and reset the conference parameters. This in-call adjustment period will be discussed in further detail below. 
     After  720 , the process transitions to  705 . From step  715 , the process  700  transitions to  725  when it determines (at  715 ) that no participant has left the conference. At  725 , the process  700  determines whether any new participant has joined the conference. If so, the focus computer sends a notification to the other participants in the conference that the new participant has joined at  730 . Based on this notification, the other participants allocate resources for decoding and displaying the new participant&#39;s data. 
     At  730 , the focus computer also performs an in-call adjustment operation, which might downgrade the conference parameters for one or more computers. For instance, the capabilities and/or bandwidth of the new participant&#39;s computer might require the focus computer to downgrade the conference parameters for the other computers. Also, the addition of the new participant might require the bandwidth that the focus point computer allocates to the other non-focus participants to be reduced below a threshold that would require one or more of the computers to redefine their conference parameters. 
     Also, at  730 , the focus and non-focus computers commence an in-call loss detection operation for a particular interval of time (e.g., for 20 seconds) after the focus computer transmits the notification at  730  or the non-focus computers receive the notification at  730 . If the detection operation of any of the computers detects packet loss, one or more conference parameters of one or more computers might be modified, as further described below. 
     After  725 , the process  700  transitions to  735 , where it determines whether the multi-participant conference is still in progress. If not, the process ends. Otherwise, the process returns back to  705 , which was described above. 
     a) In-Call Loss Detection 
     As mentioned above, some embodiments perform in-call bandwidth adjustments particularly at the start of a new conference or when a new participant joins a conference already underway.  FIG. 8  conceptually illustrates an in-call bandwidth adjustment process  800  of some embodiments. The in-call bandwidth adjustment process  800  begins at  805  when a new non-focus computer joins the conference. 
     After the new computer joins the conference, the focus and non-focus computers perform (at  810 ) an in-call loss detection operation. Such an operation is commenced when the focus point computer (at  730  of the process  700  of  FIG. 7 ) starts such an operation and instructs each non-focus computer to perform such an operation. 
     The focus computer of these embodiments may also perform in-call bandwidth detection with the other computers already in the conference. These embodiments attempt to preserve the quality of the conference for the participants by detecting the transmission quality for each participant. In these embodiments, packet loss and delay may be used as a particular measure of quality for the in-call adjustments. Although, other embodiments may employ different parameters to measure quality for the conference participants. Next, the method some embodiments employ to perform in-call bandwidth detection at  810  is described. 
     For a small time window at the beginning of a new conference or after a new participant joins a conference already in progress, each participant detects the amount of packet loss and delay at its receiver. This discussion will proceed by only referring to packet loss since packets exhibiting significant delay are considered dropped or lost during real-time transmission. For some embodiments, this small time window is approximately 15-20 seconds after acceptance by each participant joining the conference. 
     The in-call bandwidth detection at  810  might reveal that one or more participants&#39; computers detect loss. If the time window for the in-call adjustment has not elapsed at step  812 , then the process  800  checks for loss at step  814 . If the process  800  does not detect loss at  814 , then the process  800  returns to step  812  and continues to check for loss until the time elapses at step  812 , otherwise the process concludes. 
     If the process  800  detects loss at step  814 , the focus computer will then determine the type of loss at  815 . In some embodiments, the type of loss detected at  814  can be divided into four categories of loss, or states of the conference during the time window for the in-call bandwidth detection. These embodiments may then respond appropriately to the type of loss detected. These conditional states may trigger in-call adjustments that will be described in further detail below. In some embodiments, each of the four conditional states caused by a non-focus computer joining may cause the focus computer and other computers in the conference to pass additional messages to and from each other. The conferencing computers might use these messages to indicate their particular status or needs during the conference and up/downgrade the conference in response to the messages. In some embodiments, the focus computer redistributes its upload bandwidth to each computer in the conference. 
     For instance,  FIG. 8  illustrates four conditional states  825 ,  840 ,  855  and  870  that some embodiments assume, which cause these in-call adjustments based on bandwidth. Specifically, state  825  and  840  represent conditions where one or more than one non-focus computer detects loss from the focus computer, respectively. States  855  and  870  represent conditions where the focus computer detects loss from one or multiple non-focus computers, respectively. The process  800  distinguishes the conditional states by using a two step inquiry beginning at step  815 , where the process  800  determines whether the loss is from the focus point computer. If the loss is from the focus computer, the process checks whether the loss is detected by one or more than one participant at step  820 . To distinguish the case where one participant experiences loss from the case where multiple participants experience loss, the focus computer will wait for approximately 500 milliseconds after a message from a non-focus computer indicating loss from that computer to see if other computers report loss. One of ordinary skill will recognize that other embodiments will wait for a time other than 500 milliseconds. If only one participant detects loss at step  820 , then the process  800  transitions to step  825 , which is the first of the four cases discussed in detail below. 
     Examples of What to Do about Loss, Four Cases 
     Case — 1: Computer C&#39;s Download is the Bottleneck. Only Computer C detects loss from the focus computer. 
       FIG. 10  illustrates loss detected by one non-focus computer C for data from a focus computer (step  825  in  FIG. 8 ). As shown in  FIG. 10 , solid lines to and from the focus computer represent normal data transmission. However, the dashed line from the focus computer to the non-focus computer C indicates loss detected by the non-focus computer C. In this condition, the non-focus computer C of some embodiments will send a “set bit rate” packet to the focus computer (at  825 ). Thus, when only one participant detects loss, the focus computer of these embodiments adjusts the frame rate and/or the frame size (i.e., the bit rate) at the focus computer&#39;s encoder to accommodate the non-focus computer experiencing loss/difficulty with reception (at  830 ). In some embodiments, the focus computer sets its transmission bit rate to the value contained in the set bit rate packet (i.e., to the value requested by the non-focus computer detecting loss). 
     For the embodiments where the focus computer only transmits using one encoder, the focus computer&#39;s transmission will be downgraded for all participants in the particular conference. In other words, the focus computer typically sends the same bit rate (i.e., the bit rate of the most constrained participant) to all non-focus computers in these embodiments. In this case, the non-focus computer C is said to be the bottleneck for the conference (likely due to lack of sufficient download bandwidth). Should the non-focus computer C leave the conference, the focus computer of some embodiments might then re-evaluate the conference parameters to check whether it is possible to upgrade the conference for the remaining participants. 
     After the process  800  performs the in-call adjustment based on the loss detected by one non-focus computer at step  830 , the process  800  returns to step  812  to check whether the time has elapsed. In some embodiments, the process  800  repeats several times before the time has elapsed. If the time has elapsed at step  812 , the process  800  concludes. Otherwise, the process  800  proceeds to step  814  as described above. If at step  820 , however, the process  800  determines that more than one participant detects loss from the focus computer, then the process  800  transitions to step  840 . 
     Case — 2: Focus Computer&#39;s Upload is the Bottleneck, e.g., Computers A, B and C each detect packet loss from the focus computer. 
       FIG. 12  illustrates loss detected by multiple participants for data from the focus computer (step  840  in  FIG. 8 ). As shown in  FIG. 12 , solid lines represent normal data transmission, while dashed lines represent packet loss. In some embodiments, when the focus computer receives notification of loss from multiple participants (at  840 ), the focus computer resets its transmission bit rate to each participant (at  845 ). In some embodiments, each non-focus computer sends a request for a different bit rate in a set bit rate packet to the focus computer. The focus computer of these embodiments may sum the value contained in the bit rate requests and divide by the number of requests it receives to adjust its transmission bit rate. In other words, the focus computer of these embodiments sets its transmission bit rate to the average rate requested by those participants in the conference that reported loss. In these embodiments, the focus computer may adjust its transmission bit rate by adjusting the frame rate or frame size of its encoder. For the embodiments in which the focus computer only uses a single encoder, the transmission bit rates to each non-focus computer are typically equal. 
     As mentioned above, to distinguish the first case (where the participant C was the bottleneck, and the only recipient reporting loss) from the second case (where multiple recipients report loss), the focus computer of some embodiments will wait before resetting its transmission bit rate, to see how many participants report loss. The waiting period may be different in different embodiments (e.g., 500 milliseconds, one second, etc.). 
     After the process  800  makes adjustments based on loss from the focus computer detected by multiple non-focus computers at step  845 , the process  800  returns to step  812  to check whether the time has elapsed. If at step  815 , the process  800  determines that the loss is not detected from the focus computer (i.e., the loss is from one or more non-focus computers), then the process  800  transitions to step  850  to determine from how many computers the focus computer detects loss. The focus computer of some embodiments may perform this determination by using the same waiting method as described above. If only one computer detects loss at step  850 , then the process  800  transitions to step  855 . 
     Case — 3: Computer C&#39;s Upload is the Bottleneck. 
       FIG. 9  illustrates loss detected by a focus computer for data from one non-focus computer C (step  855  in  FIG. 8 ). As shown in  FIG. 9 , the solid lines to and from the focus computer indicate normal data transmission, while the dashed line from the non-focus computer C to the focus computer indicates loss (e.g., dropped or delayed packets) detected by the focus computer. When the focus computer detects loss from only one non-focus computer, the focus computer of some embodiments may send a request to that non-focus computer, in this case non-focus computer C, to lower the non-focus computer&#39;s transmission bit rate (at  855 ). In some embodiments, the request is contained in a “set bit rate” packet. The focus computer of some embodiments may request that the non-focus computer lower its transmission bit rate equal to the bit rate of the most constrained participant in the particular conference. In this case, the non-focus computer C is likely not the most constrained participant in the conference. However, reducing the computer C&#39;s transmission bit rate (at  860 ) will allow the focus computer to maintain the conference (i.e., to adequately send and receive conference data to and from all of the conference participants, including the most constrained participants). 
     Once the process  800  adjusts to the loss detected from one non-focus computer at step  860 , the process  800  returns to step  812  to check whether the time has elapsed. If the focus computer detects loss from more than one non-focus computer at step  850 , then the process  800  transitions to step  870 . 
     Case — 4: Focus Computer&#39;s Download is the Bottleneck. 
       FIG. 11  illustrates loss detected by the focus computer for data from multiple participants (step  870  in  FIG. 8 ). In  FIG. 11 , the dashed lines indicate loss of packets detected by the focus computer for data from each non-focus computer A, B and C in the conference. When the focus computer detects loss from multiple participants, the focus computer of some embodiments sends a “set bit rate” packet to all the conference participants to lower their transmission bit rates to a rate determined by the focus point (at  870 ). The focus computer of some embodiments requests the bit rate of each participant to be set at the average bit rate previously received from all the non-focus computers in the conference (at  875 ). Upon receiving the set bit rate packet from the focus computer, each non-focus computer will set its transmission bit rate to the requested bit rate. In this case, the focus computer is said to be the bottleneck in the conference. This bottleneck is likely due to insufficient download bandwidth for the focus computer. Once the process  800  adjusts the conference for this kind of loss at step  875 , the process  800  returns to step  812  to check whether the time has elapsed. As mentioned above, the process  800  may repeat several times before the time elapses at step  812 . Once the time has elapsed at step  812 , then the process  800  concludes. 
     An Example of the Three Bandwidth Adjustments for a Conference 
     At this time, it might be useful to review three possible opportunities to configure a conference based on bandwidth at three separate times for a given conference. To distinguish these three configuration phases, they are referred to as (1) static estimation, (2) dynamic determination, and (3) in-call adjustment. For instance, a focus capable participant may initially (1) estimate that it is capable of sending at about 1.0 Mbps at application startup. During invitation and acceptance of a conference, a non-focus computer and the focus computer may (2) determine that each is able to transmit and receive at about 1.0 Mbps in the conference. After which, a third participant may join the conference. The third participant may have (1) estimated its own bandwidth at 1.0 Mbps when its conferencing application started. The third participant may also (2) determine that a 1.0 Mbps conference is possible with the focus computer. 
     However, the focus computer is already conferencing at its maximum 1.0 Mbps upload with the second participant&#39;s computer. In this situation, the in-call bandwidth adjustment (3) should detect loss at either or both of the second and third participants. Upon encountering this situation, the focus computer will downgrade the conference (i.e., will divide its available 1.0 Mbps upload bandwidth between the second and third participants) to preserve the quality of the conference for all subscribed participants.  FIG. 13  illustrates an example where the focus computer divides its 1.0 Mbps upload over two non-focus computers.  FIG. 14  illustrates an example where the focus computer redistributes its 1.0 Mbps for three non-focus computers at 333 Kbps each, when a non-focus computer C joins. This example of a third participant joining a two-participant conference to form a multi-participant conference illustrates one embodiment, of an in-call bandwidth adjustment. Specifically, the focus computer performs in-call adjustment by bandwidth redistribution. The components and operation of the focus computer during a conference is discussed in Section IV. 
     III. SIP Messaging and Encryption 
     Some embodiments allow messaging over a different set of ports than the ports used for video or for audio data transmission. Some of these embodiments employ messaging over Session Initiation Protocol (SIP), which is particularly useful for setting up a conference (invitation and acceptance), and for sending messages during the conference (e.g., status updates regarding participants joining or leaving). These messages can be used for signaling setup procedures and up/down-grade procedures at various times during a conference (i.e., when participants join or leave). 
     The typical Session Initiation Protocol (SIP) packet includes a header and a body. Some embodiments add additional information to the SIP packet body by using the Session Description Protocol (SDP). SDP information may contain certain parameters useful in video encoding such as codec, frame rate, and image size. For instance, to invite to conference, the focus computer of some embodiments will send a SIP packet containing a proposed set of conference parameters that are stored in bit fields (e.g., codec, frame rate, and image size, hardware description, and conference status). Particularly novel in some embodiments is the SDP information in the invitation sent by the focus computer. In some embodiments, this SDP information includes the default image sizes for peer-to-peer and multi-participant conferences, when setting up a new conference, and for up/downgrading an existing conference. These embodiments may also include the set of standard SDP information typically required for conferencing. This set of standard SDP information is defined in the IETF specification regarding SIP. 
     As mentioned above, the messages of some embodiments include parameters such as conference status, bit rate, and hardware description, which may include machine and processor type (e.g., PowerPC G3, G4, G5, etc.), number of CPUs, and speed of CPUs. Conference status information typically includes the number of participants and/or the participants who are joining/leaving with their conferencing capabilities and hardware descriptions. 
     In these embodiments, a focus computer may send a set of proposed conferencing parameters in an invitation to conference message by using a SIP packet. The recipient of the SIP packet can compare its conference capabilities with the invitation sent by the focus computer to aid in the formulation of an acceptance message and/or the initial conference packets. As previously mentioned, these initial conference packets may include conference parameters as well as A/V data intended for the focus computer. The SIP packet recipients of these embodiments may further cache information from the received invitation message for future reference in the present conference, or even future conferences involving the particular focus computer that sent the invitation. 
     During acceptance, the client can send a confirmation SIP packet containing SDP parameters with the same conference parameters that were offered by the focus computer, or with one or more downgraded parameters (e.g., a smaller image size, a lower codec such as H.263 instead of H.264). The SDP parameters for the conference may also be adjusted at various times during a conference. For instance, the conference parameters may be downgraded when the conference changes from a two-participant to a multi-participant conference and when additional participants join the multi-participant conference. Conversely, the conference parameters may be upgraded when participants leave the conference and, specifically, when the conference changes from a multi-participant to a two-participant conference. 
     In other words, the various bandwidth measurements for the embodiments above, when used in conjunction with a set of rules, may determine the capabilities of each encoder and the availability and settings of each decoder for each participant in a conference. These capabilities and settings may form the parameters for a conference. For instance, a group of participants with G5 processors can perform videoconferencing at 320×240 resolution using the H.264 codec. More examples of these rules are illustrated in the tables of Section II of this application. The conference parameters may need to be passed or updated at various times during a conference. This task is accomplished in some embodiments through the use of SIP packets containing SDP fields to hold the “session description” information. 
     Some embodiments transmit the SIP packets over the Universal Datagram Protocol (UDP). However, a multi-participant conference may have too much hardware description and bandwidth information in the SIP packets to fit in a single UDP packet. Thus, some embodiments compress the SIP/SDP information and tags. This compression shortens attribute names, status strings, and XML tags. These embodiments allow the conference messages to continue to be relayed by using SIP over UDP. As is known in the art, UDP has particular advantages for real-time transmission, such as A/V data transmissions during multi-participant conferencing. 
     Some embodiments use an automated encryption process to securely initiate a conference and securely transmit A/V data between a focus computer and non-focus computers. This encryption process selects the type of encryption to use between the focus computer and a non-focus computer by traversing a hierarchy of encryption options based on the encryption capabilities of the focus and non-focus computers (e.g., based on whether each participant&#39;s computer supports certificate based encryption, or another method of encryption). This encryption process also pre-tabulates counter and encryption keys during system idle time (e.g., before the next packet is encoded.). During a conference, the most compute-intensive operation is the encoding of video information for transmission in packets. The encoded data packets may then be encrypted by using an encryption key. Encryption of data packets might involve applying the encryption key to a data packet through a logic function (e.g., XOR), which does not add much computation. However, calculation of the key for encryption may lengthen the time to send a data packet. Thus, some embodiments pre-calculate an encryption key in a separate process from the encoding process, before the encryption key is needed for a packet, or even before the video data for that particular packet enters the encoder. In these embodiments, one or more keys may be calculated and stored for use with the next grouping of data that is intended for encoding and packetization, after a previous packet is transmitted but before the next packet is encoded. 
     IV. Operation 
     A. Example of Focus-Point Video Conference 
       FIG. 15  illustrates an example of a video conference  1500  according to the focus-point architecture described above. In this example, a focus computer  1505  of a participant D is engaged in a video conference with three computers  1510 - 1520  of three participants A, B, and C through a network (not shown). As mentioned above, the focus computer  1505  serves as a central distributor of audio/video content during the video conference. 
     As the central distributor of audio/video content, the focus point  1505  receives A/V data from each participant, composites and encodes the A/V data, and then transmits the composite A/V data to each of the non-focus machines.  FIG. 16  shows an example of such an exchange for the four participant example of  FIG. 15 . Specifically,  FIG. 16  illustrates the focus point  1505  receiving one video frame  1615 - 1625  from each participant. 
     From the received images  1615 - 1625 , the focus point  1505  generates and transmits a composite frame to each non-focus participant. As shown in  FIG. 16 , the focus computer  1505  removes a particular non-focus participant&#39;s video frame from the composite frame that the focus computer  1505  transmits to the particular non-focus participant, in order to save bandwidth. For instance,  FIG. 16  illustrates for participant A, a composite image  1630  that does not have participant A&#39;s own image  1615 . Instead of a non-focus participant&#39;s own image, the focus computer inserts a empty-field flag  1645  in the location of the non-focus participant&#39;s image in the composite image  1630 , in order to indicate the absence of the frame corresponding to the non-participant&#39;s own image. Once each non-focus computer receives its encoded composite image, the non-focus computer decodes the composite frame, extracts each of the sub-frames in the composite frame and then displays the decoded, extracted frames on its display. Some embodiments do not use the empty-field flag  1645 , and instead simply remove the image of a particular non-focus participant from the composite image sent to the particular non-focus participant. For instance, in some embodiments, the non-focus point module&#39;s decoder determines how the video image is composed with remaining encoded sub images because each encoded macroblock in each image has an identifier that represents its location. 
     As shown in  FIG. 16 , the focus computer  1505  also mixes and encodes the audio signals  1617 ,  1622 , and  1627  that it receives from the non-focus computers, and then transmits the mixed, encoded signals  1632 ,  1637 , and  1642  to the non-focus computers. In some embodiments, the focus computer  1505  removes a particular non-focus participant&#39;s audio signal from the mixed audio signal that the focus point transmits to the particular non-focus participant, otherwise the particular non-focus participant will hear his own voice when the mixed audio is played on the participant computer&#39;s loudspeakers. Also, in some embodiments, the focus point  1505  calculates signal strength indicia for each participants&#39; audio signals, and appends the signal strength indicia to the mixed signals that it sends to each participant. The non-focus computers then use the appended signal strength indicia to display audio level meters that indicate the volume levels of the different participants, and to pan the audio across the loudspeakers of a participant&#39;s computer in order to help identify orators during the conference. 
     Some embodiments are implemented by a video conference application that can perform both focus and non-focus point operations. In some embodiments, this video conference application has two modules, a focus-point module and a non-focus point module that run on top of an operating system of a video-conference participant&#39;s computer. During a multi-participant video conference, the video conference application uses the focus-point module when this application is serving as the focus point of the conference, and uses the non-focus point module when it is not serving as the focus point. The focus-point module performs focus-point A/V processing operations when the video conference application is the focus point of a multi-participant video conference. On the other hand, the non-focus point module performs non-focus point A/V processing operations when the application is not the focus point of the conference. In some embodiments, the focus and non-focus point modules share certain resources. 
     The focus-point module of the focus computer  1505  and the non-focus point modules of the non-focus computers  1510 - 1520  are described in the sub-sections below. 
     B. Focus-Point Module&#39;s Video Codec Section 
     For some embodiments of the invention,  FIG. 17  illustrates the video codec section of the focus-point module of focus computer  1505  of  FIG. 15 .  FIG. 17  shows focus-point module as utilizing three decoders  1720 - 1730 , three intermediate buffers  1735 - 1745 , three resizers  1747 - 1749 , a local image capture module  1751 , a frame rate controller  1752 , a composite image buffer  1755 , an encoder  1760 , a redundancy remover  1765 , a perspective adjuster  1775 , and a local image controller  1785 . 
     The decoders  1720 - 1730 , the intermediate buffers  1735 - 1745 , and the resizers  1747 - 1749  form three video decoding pipelines into three sections  1757 - 1759  of the composite image buffer  1755 . These three video decoding pipelines allow the focus-point module to decode and composite video signals from non-focus computers  1510 - 1520  during the video conference. 
     Specifically, each decoder  1720 ,  1725 , or  1730  is responsible for decoding video signals from one non-focus computer during a video conference. The focus computer  1505  defines a decoder for a particular non-focus participant during the set up process when the particular non-focus focus participant joins the conference. The focus computer  1505  might subsequently change or modify this decoder as a result of subsequent in-call adjustment operations. 
     After decoding a received frame, each decoder  1720 ,  1725 , or  1730  stores the decoded frame in an intermediate buffer  1735 ,  1740 , or  1745 , which, in some embodiments, is a location in the memory of the focus-point computer. At a particular frame sampling rate, each resizer  1747 ,  1748 , or  1749  (1) retrieves a frame that is stored in its corresponding intermediate buffer, (2) resizes this frame, if such resizing is necessary, and (3) stores the frame in its corresponding section in the composite image buffer  1755 . For instance, the resizer  1748  retrieves a decoded frame of the participant B from the intermediate buffer  1740 , resizes this retrieved frame if necessary, and stores this frame in the composite-buffer section  1758 . 
     The frame rate controller  1752  defines the frame sampling rate at which the resizers  1747 - 1749  retrieve frames from the intermediate buffers  1735 - 1745 . The frame rate controller  1752  determines this rate based on a variety of factors, which may include the system bandwidth, the computational resources of the focus-point computer, the number of participants in the video conference, etc. At the frame sampling rate that the controller  1752  supplies to the resizers  1747 - 1749 , the frame rate controller  1752  also directs the local image capture module  1751  to store frames in section  1756  of the composite image buffer  1755 . These stored frames are the images of the video-conference participant who is using the focus-point computer during the video conference. These images are captured by the camera  1750  and the local image capture module  1751  at the focus-point computer. In some embodiments, the frame rate controller  1752  changes the particular frame rate during a video conference, as the conditions of the video conference change. 
     As mentioned above, the resizers  1747 - 1749  retrieve frames from the buffers  1735 - 1745  based on the frame rate they receive from the controller  1752 . Before storing a retrieved frame in the composite image buffer, a resizer resizes the retrieved frame when the non-focus computer that supplied this frame supplied it at a different size than the size of the composite-buffer section for this frame. For instance, to save bandwidth or computational resources during the encoding, a non-focus computer might encode and transmit smaller frames (i.e., encode frames at coarser level of granularity and transmit packets with less encoded content for each frame). 
     The focus computer  1505  defines the resizing operation for a particular non-focus participant during the set up process when the particular non-focus participant joins the conference. The focus computer  1505  might subsequently change or modify this resizing operation as a result of subsequent in-call adjustment operations. 
     As mentioned above, the resizers  1747 - 1749  store potentially-resized frames in their corresponding sections  1757 - 1759  of the composite image buffer  1755 . In some embodiments, the composite image buffer  1755  is a location in the memory of the focus-point computer, and each section  1756 - 1759  in this buffer is a contiguous logical section at this location in the memory. 
     At the sampling rate that the controller  1752  defines, the encoder  1760  encodes the composite frame that is stored in the composite image buffer. The encoder encodes the sub-frame that is stored in each section  1756 ,  1757 ,  1758 , or  1759  independently of the sub-frames that are stored in the other sections of the composite image buffer  1755 . The encoder  1760  decouples the encoding of each sub-frame in each section  1756 ,  1757 ,  1758 , or  1759  so that the encoding of each sub-frame does not depend on any other sub-frame (i.e., the encoding of one section does not use video data beyond the boundaries of each section). For example, the encoding of the macroblocks in the sub-frame of participant A in section  1757  does not depend on the encoding of the macroblocks in the sub-frame of participant B in the section  1758 . 
     The focus computer  1505  defines the encoder  1760  during the set up process when a video conference commences. The focus computer  1505  might subsequently change or modify this encoder as a result of subsequent in-call adjustment operations. 
     After encoding a composite frame, the encoder  1760  supplies the redundancy remover with an encoded video stream that contains each participant&#39;s encoded video data in a separate section (i.e., contains different participants encoded video data in separate, non-interleaved sections). The non-interleaved structure of the encoded stream allows the redundancy remover to remove quickly a particular non-focus participant&#39;s video data from the video stream that is to be transmitted to the particular non-focus participant. 
     Once the redundancy remover removes each participant&#39;s redundant image data from the participant&#39;s video stream, the redundancy remover transmits the participant&#39;s video stream to the participant. Accordingly,  FIG. 17  illustrates the redundancy remover  1765  sending three video streams to the three non-focus participants A, B, and C. 
       FIG. 17  also illustrates that the perspective adjuster  1775  of the focus-point module retrieves the focus point participant&#39;s image from focus point sub image  1756  in the composite image buffer  1755 . The perspective adjuster  1775  also retrieves non-focus participants sub images from the intermediate buffers  1735 ,  1740 , and  1745 . In some embodiments, this adjuster receives these frames at the frame rate specified by the frame rate controller  1752 . The adjuster  1775  adjusts each non-focus participant&#39;s frame for a perspective view on the display  1795  of the focus-point computer. It then supplies the adjusted frames to the local image controller, which then renders the frames for display on the display device  1795 . 
       FIG. 17  provides a simplified conceptual illustration of the focus-point module&#39;s decoding and encoding operations. One of ordinary skill will realize that the focus point module will have other components in other embodiments. For instance, in some embodiments, this module will have one or more modules to prevent duplicate encoding and/or decoding of an identical frame or very similar frames. These additional modules are further described in the above-incorporated U.S. Pat. No. 7,817,180, entitled “Video Processing in a Multi-Participant Video Conference”. 
     C. Non-Focus Point Module&#39;s Video Codec Section 
     For some embodiments of the invention,  FIG. 18  illustrates a non-focus video codec section  1800  of a non-focus point module of a non-focus computer  1510 ,  1515 , or  1520 . The video codec section  1800  performs encoding and decoding operations. For its encoding operation, the video codec section  1800  utilizes a local image capture module  1840 , a frame rate controller  1842 , and an encoder  1850 . For its decoding operation, the video codec section  1800  utilizes a decoder  1810 , an intermediate buffer  1815 , a perspective adjuster  1820 , and a local image controller  1830 . 
     During the video conference, a camera  1825  attached to the non-focus computer films the video-conference participant who is using the non-focus point computer. During the encoding operation, the local image capture module  1840  receives and captures video frames that are produced by the camera. At a particular sampling rate that is specified by the frame rate controller  1842 , the local image capture module  1840  directs the captured frames to the encoder  1850 , which then encodes and transmits the frames to focus-point computer. In some embodiments, the encoder  1850  and the frame rate of the controller  1842  are defined during the setup process for the non-focus computer, and are susceptible to changes through in-call adjustments during the video conference as the conference conditions change. 
     During its decoding operation, the video codec section  1800  receives composite frames from the focus point module and decodes them for display on the display device  1835  of the non-focus computer. Specifically, the decoding process begins when the video codec section  1800  receives a video stream that contains a composite frame from the focus point module. Next, the decoder  1810  decodes the received composite frame, and stores the decoded composite frame in the intermediate buffer. In some embodiments, the decoder  1810  is defined during the setup process for the non-focus computer, but might change through in-call adjustments during the video conference as the conference conditions change. 
     Each decoded composite frame includes several sub-frames, where each sub-frame represents a frame of one of the other participants in the video conference. The perspective adjuster  1820  then retrieves the decoded sub-frames from the intermediate buffer, and adjusts the perspective view of these images of the other conference participant. The adjuster  1820  supplies the adjusted frames to the local image controller  1830 . The local image controller also receives a video frame of the local non-focus point video-conference participant from the local image capture  1840 . From the adjusted frames of the other conference participants and the local participant&#39;s captured frame, the local image controller  1830  then renders the video-conference display presentation for display on the display device  1835  of the non-focus computer. 
       FIG. 18  provides a simplified conceptual illustration of the non-focus point module&#39;s decoding and encoding operations. One of ordinary skill will realize that the non-focus point module will have other components in other embodiments. For instance, in some embodiments, this module will have one or more modules to prevent duplicate encoding and/or decoding of an identical frame or very similar frames. These additional modules are further described in the above-incorporated U.S. Pat. No. 7,817,180, entitled “Video Processing in a Multi-Participant Video Conference”. 
     D. Focus-Point Module&#39;s Audio Codec Section 
     For some embodiments of the invention,  FIG. 19  illustrates an audio codec section  1900  of the focus-point module of the focus computer  1505 . The focus audio codec  1900  generates mixed audio signals for transmitting to non-focus participants, and performs audio presentation for the conference participant who is using the focus point computer during the video conference. 
     For its audio mixing operation, the focus audio codec  1900  utilizes one decoder  1925  and one intermediate buffer  1930  for each incoming audio signal, an intermediate buffer  1930  for the focus point audio signal, one audio capture module  1915 , one signal strength calculator  1980 , one audio mixer  1935  for each mixed audio signal, and one encoder  1950  for each transmitted mixed audio signal. For its audio presentation operation at the focus-point computer, the focus audio codec  1900  also utilizes one audio panning control  1960  and one level meter control  1970 . 
     During its audio mixing operation, two or more decoders  1925  receive two or more audio signals  1910  containing digital audio samples from two or more non-focus point modules. The decoders  1925  decode and store the decoded audio signals in two or more intermediate buffers  1930 . In some embodiments, the decoder  1925  for each non-focus computer&#39;s audio stream uses a decoding algorithm that is appropriate for the audio codec used by the non-focus computer. This decoder is specified during the process that sets up the audio/video conference. The decoder for each stream might change during a video conference as a result of in-call adjustment operations. 
     The focus audio codec  1900  also captures audio from the participant that is using the focus point computer, through microphone  1920  and the audio capture module  1915 . The focus audio codec stores the captured audio signal from the focus-point participant in its corresponding intermediate buffer  1930 . 
     Next, the audio signal strength calculator  1980  calculates signal strength indicia corresponding to the strength of each received signal. Audio signal strength calculator  1980  assigns a weight to each signal. In some embodiments, the audio signal strength calculator  1980  calculates the signal strength indicia as the Root Mean Square (RMS) power of the audio stream coming from the participant to the focus point. The RMS power is calculated from the following formula: 
                 R   ⁢           ⁢   M   ⁢           ⁢   S     =           ∑     i   =   1     N     ⁢       (     Sample   i     )     2       N         ,         
where N is the number of samples used to calculate the RMS power and Sample i  is the i th  sample&#39;s amplitude. The number of samples, N, that audio signal strength calculator  1980  uses to calculate RMS value depends on the sampling rate of the signal. For example, in some embodiments of the invention where the sampling rate is 8 KHz, the RMS power might be calculated using a 20 ms chunk of audio data containing 160 samples. Other sampling rates may require a different number of samples.
 
     The audio codec  1900  then utilizes the audio mixers  1935  to mix the buffered audio signals. Each audio mixer  1935  generates mixed audio signals for one of the participants. The mixed audio signal for each particular participant includes all participants&#39; audio signals except the particular participant&#39;s audio signal. Eliminating a particular participant&#39;s audio signal from the mix that the particular participant receives eliminates echo when the mixed audio is played on the participant computer&#39;s loudspeakers. 
     The mixers  1935  mix the audio signals by generating a weighted sum of these signals. To obtain an audio sample value at a particular sample time in a mixed audio signal, all samples at the particular sampling time are added based on the weight values computed by the audio signal strength calculator  1980 . In some embodiments, the weights are dynamically determined based on the calculated signal strength indicia to achieve certain objectives. Examples of such objectives include (1) the elimination of weaker signals, which are typically attributable to noise, and (2) the prevention of one participant&#39;s audio signal from overpowering other participants&#39; signals, which often results when one participant consistently speaks louder than the other or has better audio equipment than the other. In some embodiments, the mixers  1935  append the signal strength indicia of all audio signals that were summed up to generate the mixed signal. 
     Next, for the non-focus computers&#39; audio, the encoders  1950  encode the mixed audio signals and send them to their corresponding non-focus modules. Each particular encoder is specified during the process that added the non-focus computer corresponding to the particular encoder to the video conference. The encoder for each stream might change during a video conference as a result of in-call adjustment operations. 
     The mixed audio signal for the focus point computer is sent unencoded to focus point audio panning control  1960 . Also, the signal strength indicia is sent to the level meter  1970  of the focus audio codec, which then generates the appropriate volume level indicators for display on the display device  1975  of the focus point computer. 
     One of ordinary skill will realize that other embodiments might implement the focus point module differently. For instance, in some embodiments, the focus point produces a single mixed signal that includes every participant&#39;s audio. This stream along with signal strength indicia is sent to every participant. When playing this stream, a participant will mute playback if that same participant is the primary contributor. This scheme saves focus point computing time and provides echo suppression without requiring separate, distinct streams for each participant. Also, during IP multicast, the focus point stream bandwidth can be reduced. In these embodiments, the focus point has one audio mixer and one encoder. 
     E. Non Focus Point Module&#39;s Audio Codec Section 
     For some embodiments of the invention,  FIG. 20  illustrates a non-focus audio codec section  2000  of a non-focus point module of a non-focus computer  1510 ,  1515 , or  1520 . In this example, the non-focus audio codec  2000  utilizes a decoder  2005 , two intermediate buffers  2010  and  2075 , a level meter control  2020 , an audio panning control  2045 , an audio capture module  2070 , and an encoder  2080 . 
     The non-focus audio codec performs encoding and decoding operations. During the encoding operation, the audio signal of the non-focus point participant&#39;s microphone  2060  is captured by audio capture module  2070  and is stored in its corresponding intermediate buffer  2075 . The encoder  2080  then encodes the contents of the intermediate buffer  2075  and sends it to the focus point module. The encoder  2080  is specified during the process that added the non-focus computer to the particular conference. The encoder  2080  might be changed or modified during a video conference as a result of in-call adjustment operations. 
     The decoding operation of the non-focus audio codec  2000  starts when the decoder  2005  receives audio packets from the focus point module. The decoder  2005  decodes each received audio packet to obtain mixed audio data and the signal strength indicia associated with the audio data. Like the encoder  2080 , the decoder  2005  is specified during the process that added the non-focus computer to the particular conference. The decoder  2005  might be changed or modified during a video conference as a result of in-call adjustment operations. 
     The decoder  2005  saves the decoded mixed audio data and associated signal strength indicia in the intermediate buffer  2010 . The signal strength indicia are sent to level meter control  2020  to display the audio level meters on the non-focus participant&#39;s display  2030 . In a multi-participant audio/video conference, it is desirable to identify active speakers. One novel feature of the current invention is to represent the audio strengths by displaying audio level meters corresponding to each speaker&#39;s voice strength. Level meters displayed on each participant&#39;s screen express the volume level of the different participants while the mixed audio signal is being heard from the loud speakers  2055 . Each participant&#39;s volume level can be represented by a separate level meter, thereby, allowing the viewer to know the active speakers and the audio level from each participant at any time. 
     The decoded mixed audio signal and signal strength indicia stored in the intermediate buffer  2010  are also sent to the audio panning control  2045  to control the non-focus participant&#39;s loudspeakers  2055 . Audio panning helps identify the location of the currently speaking participants on the screen and produces stereo accounting for location. Some embodiments achieve audio panning through a combination of signal delay and signal amplitude adjustment. For instance, when the participant whose image is placed on the left side of the screen speaks, the audio coming from the right speaker is changed by a combination of introducing a delay and adjusting the amplitude to make the feeling that the voice is coming from the left speaker. 
     The audio and video codec operations of the focus and non-focus modules are further described in the above-incorporated patents. 
     V. Heterogeneous Multi-Participant Video Conference 
     The above described focus-point architecture can seamlessly support heterogeneous multi-participant conferencing, where different conferencing computers participate differently in the conference. For instance, some embodiments allow different non-focus computers to use different audio encoders  2080 . To facilitate such a difference, the focus-point computer  1505  would use different audio decoders  1925  for the different audio encoders  2080  of the non-focus computers. 
     Similarly, some embodiments allow different non-focus computers to use different video encoders  1850 . To facilitate such a difference, the focus-point computer  1505  would use different video decoders  1720 - 1730  for the different encoders  1850  of the non-focus computers. Some embodiments also allow different non-focus computers to provide different sized frames, by allowing the resizers  1747 - 1749  of the focus computer to resize differently the different sized frames of the non-focus computers. 
     Moreover, in some embodiments, a participant might not provide any video data to the focus computer.  FIG. 21  illustrates an example of such a situation. In this example, the conference includes four participants A, B, C, and D, with the participant D&#39;s computer serving as the focus point and the participant B&#39;s computer providing only audio data. 
     In this example, all that the focus computer  1505  would have to do would be to forego defining in its video codec a video-decoding pipeline for the participant B.  FIG. 22  illustrates an example of such a focus point video codec  2200 . As shown in  FIG. 22 , the focus point video codec  2200  includes only two video-decoding pipelines, one for the participant A and one for participant C. For the participant B&#39;s image in the composite image, the codec  2200  stores a blank image in some embodiments. In other embodiments, the codec  2200  would not even define a section in the composite image buffer  1755  for the participant B. In either approach, the composite frames that are sent to the non-focus participants will not contain any video data regarding participant B. Accordingly, no participant will show any video of participant B. 
     However, given that in this example participant B is still providing audio data, the focus point uses the audio codec  1900  of  FIG. 19 , which has an audio decoder  1925 , an intermediate audio buffer  1930 , an audio mixer  1935 , and an audio encoder  1950  for the participant B. These components decode the participant B&#39;s audio data, store this data, mix this data with the audio data of the other participants, and then encode and transmit the mixed data to other participants. 
     In some embodiments, a participant might not provide any audio or video data to the focus computer.  FIG. 23  illustrates an example of such a situation. In this example, the conference includes four participants A, B, C, and D, with the participant D&#39;s computer serving as the focus point and the participant B&#39;s computer providing no audio or video data. 
     In this example, the focus computer  1505  would not only forego defining in its video codec a video-decoding pipeline for the participant B, but also would forego defining, in its audio codec, audio decoding and mixing pipelines for the participant B.  FIG. 24  illustrates an example of such a focus point audio codec  2400 . As shown in  FIG. 24 , the focus point audio codec  2400  includes only two audio-decoding pipelines, one for the participant A and one for participant C. Also, the focus point audio codec  2400  includes only three audio mixers, one for the participant A, one for participant C, and one for the participant D. 
     The foregoing has described methods and apparatus for multi-participant conferencing. One of ordinary skill will also recognize that the invention can be embodied in other specific forms without departing from the spirit of the invention, even though the invention has been described with reference to numerous specific details. For instance, even though the embodiments described above perform the focus point designation before the set up of the video conference, other embodiments designate a focus point computer during the video conference set up. In view of the foregoing, one of ordinary skill in the art would understand that the invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the appended claims.

Metadata:
Filing Date: 20110502
Publication Date: 20120821
Grant Date: 20120821
Priority Date: 20050428
Inventors: JEONG HYEONKUK
ABUAN JOE
NORMILE JIM
SALSBURY RYAN
TUNG BERKAT SHING
Assignee: APPLE INC
CPC Classifications: [{"code": "H04Q2213/1324", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04Q3/0045", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04Q3/0045", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04Q2213/1324", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04Q2213/13093", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04N7/15", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N7/15", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04Q2213/13093", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 37234321