In this paper, a redundant picture formation algorithm that takes into account a given redundancy rate constraint is
presented for error resilient wireless video transmission without reliance on retransmissions. The algorithm assigns
priorities to MBs according to two suggested metrics and ranks macroblocks accordingly. The first metric is based on an
end-to-end distortion model and aims at maximising the reduction in distortion per redundancy bit. The end-to-end
distortion accounts for the effects of error propagation, mismatch between the primary and redundancy description and
error concealment. Macroblocks providing large distortion reduction for fewer bits spent are assigned a higher priority.
The second metric employs the variance of the motion vectors of a macroblock and those of its neighbouring blocks.
Results show that the rate distortion metric outperforms other examined metrics by up to 2dB. Moreover, gains over
existing error resilience schemes, such as LA-RDO, are presented.
This paper proposes a concealment based approach to generating the side information and estimating the correlation noise for low-delay, pixel-based, distributed video coding. The proposed method employs a macroblock pattern similar to the one used in the dispersed type FMO of H.264 for grouping the macroblocks of each frame into intra coded (key) and Wyner-Ziv groups. Temporal concealment is then used at the decoder for "concealing" the missing macroblocks (estimating the side information-predicting the Wyner-Ziv macroblocks). The actual intra coded/decoded macroblocks are used for estimating the correlation noise. The results indicate significant performance improvements relative to existing motion extrapolation based approaches (up to 25% bit rate reduction).
We propose a method of providing error resilient H.264 video over 802.11 wireless channels by using a feedback mechanism which does not incur an additional delay typically found in ARQ-type feedback. Our system uses the TCP/IP and UDP/IP protocols, located between the medium access control (MAC) layer of 802.11, and the H.264 video application layer. The UDP protocol is used to transfer time sensitive video data without delay; however, packet losses introduce excessive artifacts which propagate to subsequent frames. Error resilience is achieved by a feedback mechanism-the decoder conveys the packet-loss information as small TCP packets to the video source as negative acknowledgements. By using multiple reference frames, slice-based coding and timely intra-refresh, the encoder makes use of this feedback information to perform subsequent temporal prediction without propagating the error to future frames. We take static measurements of the actual channel and use the packet loss and delay patterns to test our algorithms. Simulations show an improvement of 0.5~5 dB in PSNR over plain UDP-based video transmission. Our method improves the overall quality of service of interactive video transmission over wireless LAN; it can be used as a
model for future media-aware wireless network protocol designs.
The EU FP6 WCAM (Wireless Cameras and Audio-Visual Seamless Networking) project aims to study, develop and validate a wireless, seamless and secured end-to-end networked audio-visual system for video surveillance and multimedia distribution applications. This paper describes the video transmission aspects of the project, with contributions in the areas of H.264 video delivery over wireless LANs.
The planned demonstrations under WCAM include transmission of H.264 coded material over 802.11b/g networks with TCP/IP and UDP/IP being employed as the transport and network layers over unicast and multicast links. UDP based unicast and multicast transmissions pose the problem of packet erasures while TCP based transmission is associated with long delays and the need for a large jitter buffer. This paper presents measurement data that have been collected at the trial site along with analysis of the data, including characterisation of the channel conditions as well as recommendations on the optimal operating parameters for each of the above transmission scenarios (e.g. jitter buffer sizes, packet error rates, etc.). Recommendations for error resilient coding algorithms and packetisation strategies are made in order to moderate the effect of the observed packet erasures on the quality of the transmitted video. Advanced error concealment methods for masking the effects of packet erasures at the receiver/decoder are also described.