Eric Setton

Transform-domain Wyner-Ziv Codec for Video

In current interframe video compression systems, the encoder performs predictive coding to exploit the similarities of successive frames. The Wyner-Ziv Theorem on source coding with side information available only at the decoder suggests that an asymmetric video codec, where individual frames are encoded separately, but decoded conditionally (given temporally adjacent frames) could achieve similar efficiency. We propose a transformdomain Wyner-Ziv coding scheme for motion video that uses intraframe encoding, but interframe decoding. In this system, the transform coefficients of a Wyner-Ziv frame are encoded independently using a scalar quantizer and turbo coder. The decoder uses previously reconstructed frames to generate side information to conditionally decode the Wyner-Ziv frames. Simulation results show significant gains above DCT-based intraframe coding and improvements over the pixel-domain Wyner-Ziv video coder.

Cross-layer design of ad hoc networks for real-time video streaming

Cross-layer design breaks away from traditional network design where each layer of the protocol stack operates independently. We explore the potential synergies of exchanging information between different layers to support real-time video streaming. In this new approach information is exchanged between different layers of the protocol stack, and end-to-end performance is optimized by adapting to this information at each protocol layer. We discuss key parameters used in the cross-layer information exchange along with the associated cross-layer adaptation. Substantial performance gains through this cross-layer design are demonstrated for video streaming.

Towards practical Wyner-Ziv coding of video

In current interframe video compression systems, the encoder performs predictive coding to exploit the similarities of successive frames. The Wyner-Ziv theorem on source coding with side information available only at the decoder suggests that an asymmetric video codec, where individual frames are encoded separately, but decoded conditionally (given temporally adjacent frames) achieves similar efficiency. We report results on a Wyner-Ziv coding scheme for motion video that uses intraframe encoding, but interframe decoding. In the proposed system, key frames are compressed by a conventional intraframe codec and in-between frames are encoded using a Wyner-Ziv intraframe coder. The decoder uses previously reconstructed frames to generate side information for interframe decoding of the Wyner-Ziv frames.

Peer-to-Peer Live Multicast: A Video Perspective

Peer-to-peer multicast is promising for large-scale streaming video distribution over the Internet. Viewers contribute their resources to a peer-to-peer overlay network to act as relays for the media streams, and no dedicated infrastructure is required. As packets are transmitted over long, unreliable multipeer transmission paths, it is particularly challenging to achieve consistently high video quality and low end-to-end delay. In this paper, we focus on error-resilient transport for peer-to-peer video streaming. The algorithms we describe are representative of three broad categories of robust video streaming schemes: forward error correction, multiple descriptions, and prioritized automatic repeat request. We analyze how these techniques can be employed for live peer-to-peer multicast and discuss their relative merits. Our results show that significant gains can be obtained when systems are designed to adapt to the encoding structure of the video streams they are transmitting. They also reveal the importance of avoiding congestion at every peer participating in the multicast to obtain a low-latency system. Finally, we provide insights as to which are the important metrics to compare different peer-to-peer streaming systems.

Congestion-optimized multi-path streaming of video over ad hoc wireless networks

We analyze the benefits of optimal multi-path routing on video streaming, in a band-limited ad hoc network. In such environments, the actions of each node can potentially impact the overall network conditions. Thus optimal routing solutions which seek to minimize congestion are attractive as they make use of the resources efficiently. For low-latency video streaming, we propose to limit the number of routes to overcome the limitations of such solutions. To predict the performance in terms of rate and distortion, we develop a model which captures the impact of quantization and packet loss on the overall video quality. Simulations are performed to illustrate the advantages of the multi-path congestion-based partitioning scheme and confirm the validity of the model.

Congestion-Distortion Optimized Video Transmission Over Ad Hoc Networks

The performance of low-latency video streaming with multipath routing over ad hoc networks is studied. As the available transmission rate of individual links in an ad hoc network is typically limited due to power and bandwidth constraints, a single node transmitting multimedia data may impact the overall network congestion and may therefore need to limit its rate while striving for the highest sustainable video quality. For this purpose, optimal routing algorithms which seek to minimize congestion by optimally distributing traffic over multiple paths are attractive. To predict the end-to-end rate-distortion tradeoff, we develop a model which captures both the impact of encoder quantization and of packet loss due to network congestion on the overall video quality. The validity of the model is confirmed by network simulations performed with different routing algorithms, latency requirements and encoding structures.

Rate-distortion optimized video peer-to-peer multicast streaming

We study peer-to-peer multicast streaming, where a source distributes real-time video to a large population of hosts by making use of their forwarding capacity rather than relying on dedicated media servers. Hosts which may disconnect at any time, therefore a robust control protocol is needed to maintain connectivity among peers. This work presents a new peer-to-peer multicast protocol and analyzes the gains that video coding and prioritized packet scheduling at the application layer can bring to the overall streaming performance. A rate-distortion model which predicts end-to-end video quality in throughput limited environments is presented and used to determine the over-provisioning necessary to avoid self-inflicted congestion. The video stream transmitted by the source contains H.264 SP and SI frames, which are used to adaptively stop error propagation due to packet loss. Distortion-optimized retransmission requests are issued by receiving hosts to recover the most important missing packets while limiting the induced congestion. Experiments for several hundred hosts simulated in NS-2 illustrate the benefits of our system. We achieve typical end-to-end delays of 1 sec, and a stable video quality with less than 2.5% of frames lost to playout interruptions.

Congestion-distortion optimized scheduling of video over a bottleneck link

Recent research on multimedia scheduling has focused on minimizing the rate-distortion cost of transmission policies. This tradeoff only partially reflects the network congestion a media stream may generate on bandwidth-limited channels. We introduce the concept of congestion-distortion optimized streaming and propose a scheduler which attempts to minimize the Lagrangian cost of end-to-end delay and media distortion. Experiments for video on a simulated network illustrate the performance of the scheduler. Compared to a state-of-the-art scheduler, the proposed algorithm reduces end-to-end delay by approximately 50% while improving the video quality by up to 3 dB.

Channel-adaptive video streaming using packet path diversity and rate-distortion optimized reference picture selection

In this paper, we present error-resilient Internet video transmission using path diversity and rate-distortion optimized reference picture selection. Under this scheme, the optimal packet dependency is determined adapting to channel characteristics and video content, to achieve a better trade-off between coding efficiency and forming independent streams to increase error resilience. Packets are sent over the selected path that minimizes the distortion, while taking advantage of path diversity. Experiments demonstrate that the proposed scheme provides significant gains over video redundancy coding and the NACK mode of conventional reference picture selection.

Content-Aware P2P Video Streaming with Low Latency

This paper describes the Stanford P2P multicast (SPPM) streaming system that employs an overlay architecture specifically designed for low delay video applications. In order to provide interactivity to the user, this system has to keep the end-to-end delay as small as possible while guaranteeing a high video quality. A set of complimentary multicast trees is maintained to efficiently relay video traffic and a congestion-distortion optimized (CoDiO) scheduler prioritizes more important video packets. Local retransmission is employed to mitigate packet loss. Real-time experiments performed on the Planet-Lab show the effectiveness of the system and the benefits of a content-aware scheduler in case of congestion or node failures.