A.M. Kondoz

Motion adaptive error resilient encoding for MPEG-4

Optimising delivery of video codecs such as MPEG-4 is vital to ensure that acceptable quality can be offered to 3G network customers. The error prone nature of mobile channels means that the video codec that is employed must be fairly robust. In the past, such research has required alteration to existing standards. Given the imminent implementation of 3G technologies, changing the standards is not a convenient option. This paper presents a technique for altering MPEG-4 encoding parameters to increase the error robustness of the output bitstream. It exploits the fact that frames with a high degree motion are often more sensitive to error than those with low amounts of motion. Using a simple model, the video packet length and number of adaptive intra refresh (AIR) blocks are varied according to the amount of motion in a frame. Simulations using a GPRS channel are presented to confirm the benefits of the proposed scheme.

Tandeming/Transcoding Issues Between MPEG-4 and H.263

Transcoding implies the translation and mapping of the syntax of one standard onto the other without the need of any further decoding and re-encoding processes. It is distinctively important for the real life scenarios where two different standards are run, such as terrestrial and mobile-satellite links. In the light of this fact, this paper presents a novel and challenging study and implementation of mapping process between the MPEG-4 bitstream syntax and the H.263 bitstream syntax. Since the transcoding process does not embrace the very time consuming decoding and encoding schemes in already significant time elapsed satellite communications, the main goal to be achieved is to keep the processing power and time as low and short as possible. It also helps improve the QoS (Quality of Service) supported by the link operators.

Video transmission over mobile satellite systems

SUMMARY Mobile satellite communication channels are characterized by long transmission delays, variation of these delays, high bit-error-rates, shadowing and the multipath e!ect which severely reduce the quality of video services. Error control techniques including feedback mechanisms, error concealment methods, forward error correction techniques and error resilience schemes are examined in this paper for achieving a highintegrity video transmission over a mobile satellite channel. The application of three di!erent error resilience algorithms, namely Turbo codes, error-resilient entropy codes and two-way decoding using reversible codes is presented. Their joint performance is also examined. Furthermore, a low-delay and low-complexity video transcoding algorithm which fully interconnects two very low bit rate video communication standards: MPEG-4 and H.263 is also elaborated. This transcoder works as a gateway tool which links two heterogeneous multimedia networks, such as a mobile satellite network and a land-based network, with negligible processing delay and complexity. Copyright ( 2000 John Wiley & Sons, Ltd.

Multi-rate variable-quality VOP shape coder

Many MPEG-4 shape coding algorithms have been formulated to provide the user with no specific control over the rate or quality of compression. These algorithms are either optimised for high quality or low bit rate. Thus a high quality optimised algorithm will be inefficient in a low bit rate application and vice versa. Hence, to achieve a highly efficient coding algorithm, a novel multi-rate variable-quality (MRVQ) video object plane (VOP) shape coder has been developed. A MRVQ VOP shape coder is an arbitrary shape coder that uses a contour detection technique to encode the row or column where the shape contour lies. It provides a range of rates that the user can choose to suit his needs. Thus, fewer bits coding the shape of a VOP can be sent on a bandwidth limited channel while sacrificing video quality. This extends the application of this technique to a wide area of research in visual communications.