Video coding

1. A method of transmitting video to one or more recipient terminals, the method comprising:

transmitting a stream of inter frame encoded video data to a recipient terminal;

during ongoing transmission of the stream to the recipient terminal, receiving a request signal from that recipient terminal;

in response to the request signal, transmitting intra frame encoded video data to the recipient terminal in association with the inter frame encoded video data; and

receiving a request from a further terminal to join the stream, and in response, transmitting the stream of inter frame encoded video data and an initial portion of intra frame encoded video data to the further terminal.

2. The method according to claim 1 , comprising:

transmitting the stream of inter frame encoded data to multiple recipient terminals;

during ongoing transmission of the stream to the recipient terminals, receiving a respective request signal from each of those multiple recipient terminals; and

in response to each of the request signals, transmitting intra frame encoded video to the respective recipient terminal in association with the inter frame encoded video data.

3. The method according to claim 2 , wherein the intra frame encoded video data is transmitted to each of the one or more recipient terminals only in response to a request signal from the respective recipient terminal and at the beginning of the stream.

4. The method according to claim 1 , comprising:

during ongoing transmission of the stream to each of the one or more recipient terminals, receiving a respective plurality of request signals at different times from each of the recipient terminals; and

in response to each of those request signals, transmitting intra frame encoded video to the respective recipient terminal in association with the inter frame encoded video data.

5. The method according to claim 1 , wherein the stream of inter frame encoded video data is transmitted substantially without periodic transmission of intra frame encoded video data.

6. The method according to claim 1 , wherein the intra frame encoded video data is transmitted in parallel with the stream of inter frame encoded video data.

7. The method according to claim 1 , wherein the request signal indicates that the respective recipient terminal has failed to receive a portion of the inter frame encoded video data.

8. The method according to claim 1 , wherein the transmission of the inter frame encoded video data and the intra frame encoded video data is over a packet-based communication network.

9. The method according to claim 8 , wherein the packet-based communication network comprises the internet.

10. The method according to claim 8 , comprising establishing a connection with the recipient terminal over said packet-based communication network using a peer-to-peer communication system, wherein the inter frame encoded video data and intra frame encoded video data is transmitted over said peer-to-peer established connection.

11. The method of transmitting video to one or more recipient terminals, the method comprising:

transmitting a stream of inter frame encoded video data to a recipient terminal;

during ongoing transmission of the stream to the recipient terminal, receiving a request signal from that recipient terminal; and

in response to the request signal, transmitting intra frame encoded video data to the recipient terminal in association with the inter frame encoded video data, the method further comprising:

generating a first stream and parallel second stream, the first stream comprising a plurality of frames of inter frame encoded video data and no more than one frame of intra frame data, and the second stream comprising a plurality of frames of intra frame encoded video data;

wherein said transmission of the stream of inter frame encoded video data comprises transmitting the first stream, and said transmission of the intra frame encoded video data comprises transmitting selected frames of the second stream.

12. The method according to claim 11 , wherein each of the frames of intra frame data in the second stream is substantially equivalent, when decoded, to a respective corresponding one of the frames of inter frame data in the first stream.

13. The method according to claim 12 , wherein each of the frames of intra frame data in the second stream is bitwise exact, when decoded, to a respective corresponding one of the frames of inter frame data in the first stream.

14. The method according to claim 11 , wherein there are fewer frames of the first stream per unit time than frames of the first stream.

15. A method of decoding received video, the method comprising:

receiving a stream of inter frame encoded video data transmitted from a transiting terminal;

during ongoing receipt of the stream from the transmitting terminal, sending a request signal to that transmitting terminal;

in response to the request signal, receiving back alternatively encoded video data from the transmitting terminal in association with the inter frame encoded video data; and

decoding the received video using the inter frame encoded video data in association with the alternatively encoded video data, and outputting the decoded video to an output device.

16. The method according to claim 15 , wherein said alternatively encoded video data is intra frame encoded video data.

17. The method according to claim 15 , wherein the sending of said request signal is trigged by failing to receive a portion of inter frame encoded data from the transmitting terminal.

18. A computer program product for transmitting video to one or more recipient terminals, the program product comprising code embodied on a non-transitory computer-readable medium and configured so as when executed on a processor to:

transmit a stream of inter frame encoded video data to a recipient terminal;

during ongoing transmission of the stream to the recipient terminal, receive a request signal from that recipient terminal; and

in response to the request signal, transmit intra frame encoded video data to the recipient terminal in association with the inter frame encoded video data; and

receive a request from a further terminal to join the stream, and in response, transmitting the stream of inter frame encoded video data and an initial portion of intra frame encoded video data to the further terminal.

19. The computer program product according to claim 18 , wherein the code is configured to:

transmit the stream of inter frame encoded data to multiple recipient terminals;

during ongoing transmission of the stream to the recipient terminals, receive a respective request signal from each of those multiple recipient terminals; and

in response to each of the request signals, transmitting alternatively encoded video to the respective recipient terminal in association with the inter frame encoded video data.

20. The computer program product according to claim 19 , wherein the code is configured to:

during ongoing transmission of the stream to each of the one or more recipient terminals, receive a respective plurality of request signals at different times from each of the recipient terminals; and

in response to each of those request signals, transmit alternatively encoded video to the respective recipient terminal in association with the inter frame encoded video data.

21. The computer program product according to claim 19 , wherein the code is configured to transmit intra frame encoded video data to each of the recipient terminals only in response to a request signal from the respective recipient terminal and at the beginning of the stream.

22. The computer program product according to claim 18 , wherein the code is configured to transmit the stream of inter frame encoded video data substantially without periodic transmission of intra frame encoded video data.

23. A computer program product for decoding received video, the program product comprising code embodied on a non-transitory computer-readable medium and configured so as when executed on a processor to:

receive a stream of inter frame encoded video data transmitted from a transiting terminal;

during ongoing receipt of the stream from the transmitting terminal, send a request signal to that transmitting terminal; and

in response to the request signal, receive back alternatively encoded video data from the transmitting terminal in association with the inter frame encoded video data; and

decode the received video using the inter frame encoded video data in association with the alternatively encoded video data, and output the decoded video to an output device.

24. The computer program product according to claim 23 , wherein the alternatively encoded video data comprises intra frame encoded video data.

25. A transmitter for transmitting video to one or more recipient terminals, the transmitter comprising:

a transceiver arranged to transmit a stream of inter frame encoded video data to a recipient terminal and, during ongoing transmission of the stream to the recipient terminal, to receive a request signal from that recipient terminal; and

an encoder coupled to the transceiver and configured to transmit, in response to the request signal, intra frame encoded video data to the recipient terminal in association with the inter frame encoded video data;

the transceiver configured to receive a request from a further terminal to join the stream, and in response, transmitting the stream of inter frame encoded video data and an initial portion of intra frame encoded video data to the further terminal.

26. The transmitter according to claim 25 , wherein:

the transceiver is configured to transmit the stream of inter frame encoded data to multiple recipient terminals and, during ongoing transmission of the stream to the recipient terminals, to receive a respective request signal from each of those multiple recipient terminals; and

the encoder is configured to transmit, in response to each of the request signals, intra frame encoded video to the respective recipient terminal in association with the inter frame encoded video data.

27. The transmitter according to claim 26 , wherein:

the transceiver is configured to, during ongoing transmission of the stream to each of the one or more recipient terminals, receive a respective plurality of request signals at different times from each of the recipient terminals; and

the encoder is configured to transmit, in response to each of those request signals, intra frame encoded video to the respective recipient terminal in association with the inter frame encoded video data.

28. The transmitter according to claim 26 , wherein the encoder is configured to transmit intra frame encoded video data is transmitted to each of the recipient terminals only in response to a request signal from the respective recipient terminal and at the beginning of the stream.

29. The transmitter according to claim 25 , wherein transceiver is configured to transmit the stream of inter frame encoded video data substantially without periodic transmission of intra frame encoded video data.

30. A receiver for decoding received video, the receiver comprising:

a transceiver arranged to receive a stream of inter frame encoded video data transmitted from a transiting terminal; and

a decoder coupled to the transceiver and configured to send, during ongoing receipt of the stream from the transmitting terminal, a request signal to that transmitting terminal;

wherein the transceiver is arranged to receive back, in response to the request signal, alternatively encoded video data from the transmitting terminal in association with the inter frame encoded video data; and

the decoder is configured to decode the received video using the inter frame encoded video data and alternatively encoded video data, and output the decoded video to an output device.

31. The receiver according to claim 30 , wherein the alternatively encoded video data is intra frame encoded video data.

32. A computer program product for transmitting video to one or more recipient terminals, the program product comprising code embodied on a non-transitory computer-readable medium and configured so as when executed on a processor to:

transmit a stream of inter frame encoded video data to a recipient terminal;

during ongoing transmission of the stream to the recipient terminal, receive a request signal from that recipient terminal;

in response to the request signal, transmit intra frame encoded video data to the recipient terminal in association with the inter frame encoded video data; and

generate a first stream and parallel second stream, the first stream comprising a plurality of frames of inter frame encoded video data and no more than one frame of intra frame data, and the second stream comprising a plurality of frames of intra frame encoded video data;

wherein said transmission of the stream of inter frame encoded video data comprises transmitting the first stream, and said transmission of the intra frame encoded video data comprises transmitting selected frames of the second stream.

33. A transmitter for transmitting video to one or more recipient terminals, the transmitter comprising:

a transceiver arranged to transmit a stream of inter frame encoded video data to a recipient terminal and, during ongoing transmission of the stream to the recipient terminal, to receive a request signal from that recipient terminal; and

an encoder coupled to the transceiver and configured to transmit, in response to the request signal, intra frame video data to the recipient terminal in association with the inter frame encoded video data, the encoder configured to:

generate a first stream and parallel second stream, the first stream comprising a plurality of frames of inter frame encoded video data and no more than one frame of intra frame data, and the second stream comprising a plurality of frames of intra frame encoded video data;

wherein said transmission of the stream of inter frame encoded video data comprises transmitting the first stream, and said transmission of the intra frame encoded video data comprises transmitting selected frames of the second stream.