Very low-bit-rate segmentation-based video coding using contour andtexture prediction

The most efficient video coding standard for low bit rates (around 64 kb/s) is the H.261 algorithm recommended by ITU-TS. However, in certain applications such as mobile audiovisual communications and videophone through PSTN, the available transmission bandwidth is very limited. Therefore codecs working at very low bit rates are required. The paper presents a segmentation-based video coding algorithm that can work at rates as low as 10 kb/s. A novel representation of the contour information using a number of control points is proposed to estimate the contour shapes and locations from the previous frame by using the motion information. The texture parameters are also predicted and only the residual values are entropy coded. In addition two novel postprocessing techniques for edge-profile smoothing and jagged-edge rectification are described     

Entropy coding of ITU G.728 speech parameters for low bit rateaudiovisual communications

Entropy coding principles are applied to the 16 kbit/s ITU G.728 speech codec. It is shown that the average bit rate can be reduced to 14.5 kbit/s without a significant increase in the codec complexity. In very low bit rate audiovisual communication applications such as the videophone, the saved bits can be used to improve the output video quality     

Closed-loop motion compensation for video coding standards

In the classical block-matching motion-estimation approach, the motion vectors which result in minimum distortion between the estimated and the actual image block are chosen. However, these motion vectors may not be optimal in terms of coding efficiency. An analysis by synthesis method which selects the optimal motion vectors, using the resulting bit rate and distortion, is presented. A significant reduction in bit rate is achieved with virtually no degradation in objective image quality. H.263 is used in simulation experiments to test the algorithm     

Rate control feedback mechanism for packet video networks

The authors incorporate a newly proposed rate control feedback mechanism (RCFM) in an H.263 video coder. RCFM adapts to network conditions to locally drop video packets and then discard corresponding macroblocks (MBs) from any further prediction process. The proposed RCFM regulates the output bitrate of an H.263 codec while keeping all encoder parameters fixed and maintaining a good QoS     

Improved performance H.263 under erroneous transmission conditions

The authors present an algorithm for limiting the propagation of errors in an H.263 video bit stream subject to channel degradation. The frequency of occurrence of INTRA coded frames (I-frame) is increased to thwart the temporal dependency of predicted frames (P-frame). The proposed algorithm ensures that all R-bit length INTRADC coefficients of I-frames are received by inducing a change in their order of transmission. To combat the effect of channel corruption on INTRADC coefficients, a half rate convolutional coder is used. The synchronisation is protected by sending synch words at fixed-length intervals within the bit stream. Results showed that the proposed algorithm improved the quality of service (QoS) of the video coder on both the subjective and objective scales, even when similar target bit-rates are considered