Systems and methods for error resilience and random access in video communication systems

A system for media communications between a transmitting endpoint and one or more receiving endpoint(s) over a communications network, the network having one or more layered media transport link(s) including a more reliable media transport link to or from each endpoint, the system comprising:

• an encoder which encodes transmitted media as frames in a threaded coding structure having a number of different frame types, the frames including a sequence of reference frames;
• a decoder which decodes received media based on reference frames therein;
• a particular select subset of the frames in the threaded coding structure that is designated as a type (“R”) for reliable transport to the one or more receiving endpoint(s) over the more reliable transport link,
• wherein the subset of the frames of the type R is particularly selected to include at least the frames of the lowest temporal layer in the threaded coding structure and such that the decoder can decode at least a portion of the received media based on a reliably received frame of the type R after packet loss or error and thereafter is synchronized with the encoder;
• and
• at least one bridge that is coupled to the transmitting endpoint and to the one or more receiving endpoint(s) so that media communication between the transmitting endpoint and the one or more receiving endpoint(s) occurs through the at least one bridge, the at least one bridge being configured to reliably receive the subset of the frames of the type R from the transmitting endpoint, and reliably deliver the subset of the frames of the type R to the one or more receiving endpoint(s),
• wherein the at least one bridge retransmits a reference frame of the type R over a connection to a receiving endpoint or another bridge which is congested and is consistently dropping media packets, but reports positive receipt of the reference frame of the type R to the transmitting endpoint, whereby communications to other receiving endpoints and bridge are not affected by the connection which is congested.

A system for media communications between a transmitting endpoint and one or more receiving endpoint(s) over a communications network, the network having one or more layered media transport link(s) including a more reliable media transport link to or from each endpoint, the system comprising:

• an encoder which encodes transmitted media as frames in a threaded coding structure having a number of different frame types, the frames including a sequence of reference frames;
• a decoder which decodes received media based on reference frames therein;
• a particular select subset of the frames in the threaded coding structure that is designated as a type (“R”) for reliable transport to the one or more receiving endpoint(s) over the more reliable transport link,
• wherein the subset of the frames of the type R is particularly selected to include at least the frames of the lowest temporal layer in the threaded coding structure and such that the decoder can decode at least a portion of the received media based on a reliably received frame of the type R after packet loss or error and thereafter is synchronized with the encoder;
• and at least one bridge that is coupled to the transmitting endpoint and to the one or more receiving endpoint(s) so that media communication between the transmitting endpoint and the one or more receiving endpoint(s) occurs through the at least one bridge, the at least one bridge being configured to reliably receive the subset of the frames of the type R from the transmitting endpoint, and reliably deliver the subset of the frames of the type R to the one or more receiving endpoint(s),
• wherein the at least one bridge and/or transmitting endpoint caches an intra frame of the lowest temporal layer frames and transmits the intra frame to a receiving endpoint or another bridge in response to packet loss or in response to a new receiving endpoint joining a communication session, and
• wherein the transmitting encoder uses periodic intra macroblocks to facilitate drift elimination after the intra frame sent by the at least one bridge is used by the receiving endpoint.

A system for media communications between a transmittin endpoint and one or more receiving endpoint(s) over a communications network, the network having one or more layered media transport link(s) including a more reliable media transport link to or from each endpoint, the system comprising:

• an encoder which encodes transmitted media as frames in a threaded coding structure having a number of different frame types, the frames including a sequence of reference frames;
• a decoder which decodes received media based on reference frames therein;
• and
• a particular select subset of the frames in the threaded coding structure that is designated as a type (“R”) for reliable transport to the one or more receiving endpoint(s) over the more reliable transport link,
• wherein the subset of the frames of the type R is particularly selected to include at least the frames of the lowest temporal layer in the threaded coding structure and such that the decoder can decode at least a portion of the received media based on a reliably received frame of the type R after packet loss or error and thereafter is synchronized with the encoder, and
• wherein reliable transport of the reference frames of the type R comprises retransmissions over the more reliable transport link, and wherein the decoder resynchronizes with the encoder after an error, or synchronizes with the encoder upon entering a communication session as a new participant, by promptly decoding all retransmitted lowest temporal layer frames even if they are received too late to be currently displayed.

A method for media communications between a transmitting endpoint and one or more receiving endpoint(s) over a communications network, the network having one or more layered media transport link(s) including a more reliable media transport link to or from each endpoint, the endpoints including:

• an encoder which encodes transmitted media as frames in a threaded coding structure having a number of different frame types, the frames including a sequence of reference frames;
• and
• a decoder which decodes received media based on reference frames therein;
• the method comprising:
• designating a particular select subset of the frames in the threaded coding structure as a type (“R”) for reliable transport to the decoder over the more reliable transport link,
• wherein the subset of the frames of the type R is particularly selected to include at least the frames of the lowest temporal layer in the threaded coding structure and such that the decoder can decode at least a portion of the received media based on a reliably received frame of the type R after packet loss or error and thereafter is synchronized with the encoder;
• sending the frames of the type R to the decoder, wherein the particular select subset of the frames that is designated as a type R for reliable transport to the decoder over the more reliable transport link comprises intra and inter macroblocks;
• and
• recalculating the allocation of intra macroblocks in coding future pictures in response to packet loss or a new endpoint joining a current communication session.

A method for media communications between a transmitting endpoint and one or more receiving endpoint(s) over a communications network, the network having one or more layered media transport link(s) including a more reliable media transport link to or from each endpoint, the endpoints including:

• an encoder which encodes transmitted media as frames in a threaded coding structure having a number of different frame types, the frames including a sequence of reference frames;
• and
• a decoder which decodes received media based on reference frames therein;
• the method comprising:
• designating a particular select subset of the frames in the threaded coding structure as a type (“R”) for reliable transport to the decoder over the more reliable transport link,
• wherein the subset of the frames of the type R is particularly selected to include at least the frames of the lowest temporal layer in the threaded coding structure and such that the decoder can decode at least a portion of the received media based on a reliably received frame of the type R after packet loss or error and thereafter is synchronized with the encoder;
• sending the frames of the type R to the decoder, wherein at least one bridge is coupled to the transmitting endpoint and to the one receiving endpoint(s) so that media communication occurs through the at least one bridge;
• reliably receiving the subset of the frames of the type R from the transmitting endpoint and reliably delivering the subset of the frames of the type R to the one or more receiving endpoint(s);
• and
• retransmitting a reference frame of the type R over a connection to a receiving endpoint or another bridge which is congested and is consistently dropping media packets, but reports positive receipt of the reference frame of the type R to the transmitting endpoint, whereby communications to other receiving endpoints and bridge are not affected by the connection which is congested.

A method for media communications between a transmitting endpoint and one or more receiving endpoint(s) over a communications network, the network having one or more layered media transport link(s) including a more reliable media transport link to or from each endpoint, the endpoints including:

• an encoder which encodes transmitted media as frames in a threaded coding structure having a number of different frame types, the frames including a sequence of reference frames;
• and
• a decoder which decodes received media based on reference frames therein;
• the method comprising:
• designating a particular select subset of the frames in the threaded coding structure as a type (“R”) for reliable transport to the decoder over the more reliable transport link,
• wherein the subset of the frames of the type R is particularly selected to include at least the frames of the lowest temporal layer in the threaded coding structure and such that the decoder can decode at least a portion of the received media based on a reliably received frame of the type R after packet loss or error and thereafter is synchronized with the encoder;
• sending the frames of the type R to the decoder, wherein at least one bridge is coupled to the transmitting endpoint and to the one receiving endpoint(s) so that media communication occurs through the at least one bridge;
• reliably receiving the subset of the frames of the type R from the transmitting endpoint and reliably delivering the subset of the frames of the type R to the one or more receiving endpoint(s);
• caching an intra frame of the lowest temporal layer frames at the at least one bridge and/or transmitting endpoint;
• in response to packet loss or in response to new receiving endpoint joining a communication session, transmitting the intra frame to a receiving endpoint or another bridge;
• and
• using at the transmitting encoder periodic intra macroblocks to facilitate drift elimination after intra picture sent by the at least one bridge is used by the receiving endpoint.

A method for media communications between a transmitting endpoint and one or more receiving endpoint(s) over a communications network, the network having one or more layered media transport link(s) including a more reliable media transport link to or from each endpoint, the endpoints including:

• an encoder which encodes transmitted media as frames in a threaded coding structure having a number of different frame types, the frames including a sequence of reference frames;
• and
• a decoder which decodes received media based on reference frames therein;
• the method comprising:
• designating a particular select subset of the frames in the threaded coding structure as a type (“R”) for reliable transport to the decoder over the more reliable transport link,
• wherein the subset of the frames of the type R is particularly selected to include at least the frames of the lowest temporal layer in the threaded coding structure and such that the decoder can decode at least a portion of the received media based on a reliably received frame of the type R after packet loss or error and thereafter is synchronized with the encoder;
• sending the frames of the type R to the decoder, wherein reliable transport of the reference frames of the type R comprises retransmissions over the more reliable transport link;
• and
• after an error, or upon entering a communication session as a new participant, promptly decoding all retransmitted lowest temporal layer pictures at the decoder even if they are received too late to be currently displayed, so that the decoder is synchronized with the encoder.