Abstract: In one embodiment, a method includes receiving at a multimedia transformation unit, media streams from a plurality of endpoints, transmitting audio components of the media streams to a multipoint conferencing unit, receiving an identifier from the multipoint conferencing unit identifying one of the media streams as an active speaker stream, processing at the multimedia transformation unit, a video component of the active speaker stream, and transmitting the active speaker stream to one or more of the endpoints without transmitting the video component to the multipoint conferencing unit. An apparatus is also disclosed.

Abstract: Multimedia information communicated between a transmitter and a receiver may be transcoded by intercepting the multimedia information within a network communication system. The available transmission rate of the downlink channel may be estimated by, for example, calculating a ratio of the smoothed round trip time of packets communicated to the receiver and a smoothed congestion window associated with the downlink channel. If the transmission rate at which the multimedia information is encoded is greater than the available transmission rate, the multimedia information may be transcoded to conform the multimedia information to the available transmission rate. The transcoded multimedia information may then be transmitted to the receiver over the downlink channel using a transmission timer.

Abstract: An open loop encoding architecture encodes a sequence of interlaced video frames at macroblock level. In one aspect, each frame is divided into pairs of macroblocks and the macroblock pairs are encoded as either separate macroblocks or as two fields, depending upon a motion threshold. Predictors for the macroblock pairs may be selected from different frames in the sequence, or from frames of different resolution. In another aspect, a frame may be open loop encoded at field level instead of at macroblock level. A corresponding inverse open loop encoding architecture is used to decode the encoded frames.

Abstract: Adaptive joint source channel coding associates multiple predictors with a reference data unit, such as a macroblock or frame of video data. An encoder determines a sub-codebook in which each of the selected multiple predictors decodes to the reference data unit. An identifier for the sub-codebook is transmitted through a channel to a decoder for subsequent decoding of the reference data unit. The reference data unit itself does not need to be sent. The multiple predictors are contained within a decoding region and the identifier for the sub-codebook specifies the decoding region. The decoder uses the identified sub-codebook and one of the predictors to decode the reference data unit. If none of the original predictors are correctly received, different types of error handling are employed based on the type of channel.

Abstract: Adaptive joint source channel coding associates multiple predictors with a reference data unit, such as a macroblock or frame of video data. An encoder determines a sub-codebook in which each of the selected multiple predictors decodes to the reference data unit. An identifier for the sub-codebook is transmitted through a channel to a decoder for subsequent decoding of the reference data unit. The reference data unit itself does not need to be sent. The multiple predictors are contained within a decoding region and the identifier for the sub-codebook specifies the decoding region. The decoder uses the identified sub-codebook and one of the predictors to decode the reference data unit. If none of the original predictors are correctly received, different types of error handling are employed based on the type of channel.

Abstract: Image data encoded in accordance with a block transform coding scheme may be processed by estimating from the encoded image data a discontinuity threshold for detecting artificial edges introduced by the block transform coding scheme. Once the encoded image data is decoded, differences between pairs of pixels disposed along a block boundary of the decoded image may be determined. If the difference between a given pair of pixels is less than the discontinuity threshold, the given pair of pixels may be adjusted to reduce the difference below a visibility threshold, thereby improving the quality of the decoded image by reducing or eliminating blocking artifacts.

Abstract: Multimedia information communicated between a transmitter and a receiver may be transcoded by intercepting the multimedia information within a network communication system. The available transmission rate of the downlink channel may be estimated by, for example, calculating a ratio of the smoothed round trip time of packets communicated to the receiver and a smoothed congestion window associated with the downlink channel. If the transmission rate at which the multimedia information is encoded is greater than the available transmission rate, the multimedia information may be transcoded to conform the multimedia information to the available transmission rate. The transcoded multimedia information may then be transmitted to the receiver over the downlink channel using a transmission timer.

Abstract: Method and apparatus for image transmission using arithmetic coding, based on continuous error detection uses a controlled amount of added redundancy. A continuous error detection scheme is provided, wherein there is a trade-off between the amount of added redundancy and the time needed to detect an error once it occurs. Herein, there is no need for the cyclic redundancy check (CRC) to wait until an entire block of data has been received and processed before an error can be detected. The invention can be used to great advantage both in the automatic repeat request (ARQ) and other concatenated coding schemes. Errors in the received bit stream are detected by introducing added redundancy, e.g., a forbidden symbol, in the arithmetic coding operation. The forbidden symbol is never intended to be encoded. The redundancy error causes loss of synchronization, which is used to detect errors. If a forbidden symbol gets decoded, it means that an error has occurred.