Video Call Set Up in an Established Audio Call

1. A method performed by data processing apparatus, the method comprising: initiating, by a first endpoint and through a call server, an audio call with a second endpoint; after the audio call is established, transmitting, by the first endpoint and independent of the call server, first information specifying a video communication capability of the first endpoint that the call server did not setup in the established audio call, wherein said first information specifying a video communication capability of the first endpoint is transmitted over a real-time control protocol (RTCP) channel of the audio call; receiving, by the first endpoint, second information specifying that the second endpoint has the video communication capability; and establishing, by the first endpoint and based on the first information and second information, video communication between the first endpoint and the second endpoint independent of the call server.

2. The method of claim 1 , wherein initiating an audio call with a second endpoint comprises sending an invitation including a first set of call parameters to the call server, the method further comprising: receiving, from the call server, a second set of call parameters for transmitting audio to the second endpoint, the second set of parameters not including a full set of parameters necessary to transmit video to the second endpoint; and transmitting an acknowledgment to the call server.

3. The method of claim 1 , wherein: receiving second information specifying that the second endpoint has the video communication capability comprises receiving the second information over the RTCP channel.

4. The method of claim 3 , wherein: transmitting first information comprises transmitting a first set of video codecs that the first endpoint uses to transmit video; receiving second information comprises receiving a second set of video codecs that the second endpoint uses to transmit video; and establishing the video communication comprises selecting a video codec that is included in each of the first set of video codecs and a second set of video codecs.

5. The method of claim 1 , wherein establishing the video communication independent of the call server comprises establishing the video communication between the first endpoint and the second endpoint over the RTCP channel.

6. The method of claim 1 , wherein establishing the video communication comprises establishing a video communication over which whiteboard data are transmitted.

7. The method of claim 1 , wherein establishing the video communication independent of the call server comprises negotiating, by the first endpoint and the second endpoint and over a channel that bypasses the call server, the parameters that will be used to setup a video call between the first endpoint and the second endpoint.

8. A communications endpoint comprising: a data storage device storing information specifying a video communication capability of the communications endpoint; and one or more data processors that interact with the data storage device and execute instructions that cause the communications endpoint to perform operations comprising: initiating, through a call server, an audio call with a called endpoint; after the audio call is established, transmitting, by the communications endpoint and independent of the call server, first information specifying a video communication capability of the communications endpoint that the call server did not setup in the established audio call, wherein said first information specifying a video communication capability of the communications endpoint is transmitted over a real-time control protocol (RTCP) channel of the audio call; receiving, by the communications endpoint, second information specifying that the called endpoint has the video communication capability; and establishing, by the communications endpoint and based on the first information and second information, video communication between the communications endpoint and the called endpoint independent of the call server.

9. The communications endpoint of claim 8 , wherein initiating an audio call with a called endpoint comprises sending an invitation including a first set of call parameters to the call server, wherein execution of the instructions cause the communications endpoint to perform operations comprising: receiving, from the call server, a second set of call parameters for transmitting audio to the called endpoint, the second set of parameters not including a full set of parameters necessary to transmit video to the called endpoint; and transmitting an acknowledgment to the call server.

10. The communications endpoint of claim 8 , wherein: receiving second information specifying that the called endpoint has the video communication capability comprises receiving the second information over the RTCP channel.

11. The communications endpoint of claim 10 , wherein: transmitting first information comprises transmitting a first set of video codecs that the communications endpoint uses to transmit video; receiving second information comprises receiving a second set of video codecs that the called endpoint uses to transmit video; and establishing the video communication comprises selecting a video codec that is included in each of the first set of video codecs and a second set of video codecs.

12. The communications endpoint of claim 8 , wherein establishing the video communication independent of the call server comprises establishing the video communication between the communications endpoint and the called endpoint over the RTCP channel.

13. The communications endpoint of claim 8 , wherein establishing the video communication comprises establishing a video communication over which whiteboard data are transmitted.

14. The communications endpoint of claim 8 , wherein establishing the video communication independent of the call server comprises negotiating, by the communications endpoint and the called endpoint and over a channel that bypasses the call server, the parameters that will be used to setup a video call between the communications endpoint and the called endpoint.

15. A non-transitory computer storage medium encoded with instructions that when executed by one or more data processing apparatus cause the one or more data processing apparatus to perform operations comprising: initiating, by a first endpoint and through a call server, an audio call with a second endpoint; after the audio call is established, transmitting, by the first endpoint and independent of the call server, first information specifying a video communication capability of the first endpoint that the call server did not setup in the established audio call, wherein said first information specifying a video communication capability of the communications endpoint is transmitted over a real-time control protocol (RTCP) channel of the audio call; receiving, by the first endpoint, second information specifying that the second endpoint has the video communication capability; and establishing, by the first endpoint and based on the first information and second information, video communication between the first endpoint and the second endpoint independent of the call server.

16. The computer storage medium of claim 15 , wherein initiating an audio call with a second endpoint comprises sending an invitation including a first set of call parameters to the call server, wherein execution of the instructions cause the one or more data processing apparatus to perform operations comprising: receiving, from the call server, a second set of call parameters for transmitting audio to the second endpoint, the second set of parameters not including a full set of parameters necessary to transmit video to the second endpoint; and transmitting an acknowledgment to the call server.

17. The computer storage medium of claim 15 , wherein: receiving second information specifying that the second endpoint has the video communication capability comprises receiving the second information over the RTCP channel.

18. The computer storage medium of claim 17 , wherein: transmitting first information comprises transmitting a first set of video codecs that the first endpoint uses to transmit video; receiving second information comprises receiving a second set of video codecs that the second endpoint uses to transmit video; and establishing the video communication comprises selecting a video codec that is included in each of the first set of video codecs and a second set of video codecs.

19. The computer storage medium of claim 15 , wherein establishing the video communication independent of the call server comprises establishing the video communication between the first endpoint and the second endpoint over the RTCP channel.

20. The computer storage medium of claim 15 , wherein establishing the video communication comprises establishing a video communication over which whiteboard data are transmitted.