We review the Stanford peer-to-peer multicast (SPPM) protocol for live video streaming and report recent extensions. SPPM has been designed for low latency and robust transmission of live media by organizing peers within multiple complementary trees. The recent extensions to live streaming are time-shifted streaming, interactive region-of-interest (IRoI) streaming, and streaming to mobile devices. With time-shifting, users can choose an arbitrary beginning point for watching a stream, whereas IRoI streaming allows users to select an arbitrary region to watch within a high-spatial-resolution scene. We extend the live streaming to mobile devices by addressing challenges due to heterogeneous displays, connection speeds, and decoding capabilities.

In the above titled paper (ibid., vol. 18, no. 10, pp. 1347-1360, Oct 08), Fig. 4 was printed incorrectly. The correct figure is presented here.

We propose peer swapping as a means to improve the throughput of structured-overlay-based peer-to-peer (P2P) streaming systems. In many P2P streaming systems, an overlay is incrementally constructed as peers join the system. When the system is dominated by peers with low uplink bandwidth (so-called leeches), the overlay can get clogged, which hampers its growth. A P2P system that suffers from clogging cannot scale any longer because even peers with high bandwidth are rejected. We first provide a theoretical analysis of clogging, which reveals that clogging is inevitable in a structured-overlay-based streaming system with heterogeneous peer uplink bandwidths. To overcome clogging, we propose distributed peer swapping, a method to reconfigure the overlay without centralized control. Experimental results demonstrate that peer swapping enables the system to accept more peers by mitigating clogging.

Video streaming with virtual pan/tilt/zoom functionality allows the viewer to watch arbitrary regions of a high-spatial-resolution scene. In our proposed system, the user controls his region-of-interest (ROI) interactively during the streaming session. The relevant portion of the scene is rendered on his screen immediately. An additional thumbnail overview aids his navigation. We design a peer-to-peer (P2P) multicast live video streaming system to provide the control of interactive region-of-interest (IROI) to large populations of viewers while exploiting the overlap of ROIs for efficient and scalable delivery. Our P2P overlay is altered on-the-fly in a distributed manner with the changing ROIs of the peers. The main challenges for such a system are posed by the stringent latency constraint, the churn in the ROIs of peers and the limited bandwidth at the server hosting the IROI video session. Experimental results with a network simulator indicate that the delivered quality is close to that of an alternative traditional unicast client-server delivery mechanism yet requiring less uplink capacity at the server.

We design a test methodology to analyze in detail the video quality received at each peer in a peer-to-peer (P2P) video streaming system. The metrics that we employ at each peer include video PSNR, statistical analysis of frame-freeze events, the amount of time to wait before video playback starts, nature of the data-paths established to serve the peer, protocol overhead and duplicate data received. These metrics are estimated by analyzing the packet reception times at each peer and utilizing information about the original uncompressed video as well as the encoded video. We use this framework to compare the performance of three P2P video streaming systems by deploying them on our controlled traffic-shaped network test-bed. We can emulate the same network conditions and peer behavior for testing different systems and ensure that the experiments are repeatable. These measurements highlight the differences between systems based upon their underlying implementation, overlay architecture, and choice of protocols. This measurement study helps to gauge the performance of currently available P2P video streaming systems and points out desirable performance improvements.

We propose an overlay consisting of multiple trees with moderate outdegree to reduce end-to-end transmission delays in P2P media streaming systems. In real-time media streaming, lower end-to-end delays lead to less waiting time before playback and hence improve interactivity. A theoretical analysis of degree-bounded trees reveals that an optimal number of multiple trees can be chosen by considering the trade-off between the total propagation delay and the queueing delay experienced at intermediate peers. A distributed protocol is presented that allows peers to build multiple degree-bounded trees. From extensive packet-level simulations, we observe that the worst end-to-end transmission delay is minimized when the peerpsilas outdegree, or fan-out, is between 4 and 6 for realistic simulation parameters. This matches well with the predictions from our analysis.

We evaluate the performance of a large-scale live P2P video multicast session comprising more than 120, 000 peers on the Internet. Our analysis highlights P2P video multicast characteristics such as high bandwidth requirements, high peer churn, low peer persistence in the P2P multicast system, significant variance in the media stream quality delivered to peers, relatively large channel start times, and flash crowd effects of popular video content. Our analysis also indicates that peers are widely spread across the IP address space, spanning dozens of countries and hundreds of ISPs and Internet ASes. As part of the P2P multicast evaluation several QoS measures such as fraction of stream blocks correctly received, number of consecutive stream blocks lost, and channel startup time across peers. We correlate the observed quality with the underlying network and with peer behavior, suggesting several avenues for optimization and research in P2P video multicast systems.

We investigate retransmission-based robust video streaming over lossy packet networks in this paper. We propose to send a thumbnail video along with the video packets. The thumbnail video is Wyner-Ziv-coded to exploit its correlation with the primary video. The receiver decodes the primary video with the help of error concealment to mitigate packet losses. Upon receiving and successfully decoding the thumbnail, the receiver can estimate the local distortion due to packet losses and make intelligent decisions on which packets are needed for retransmission. Additional gain in video quality can be achieved by using the thumbnail to aid error concealment. Our experimental results demonstrate gains over previously proposed distortion-unaware heuristic methods.

We consider the general scenario where content hosted by the server comprises streams and each peer can subscribe one or more streams. Multiple multicast trees are built to deliver the streams to respective peers while exploiting the overlap of their interests for efficient and scalable delivery. We propose an optimization framework for allocating server bandwidth to minimize distortion across the peer population. We apply the framework to a novel application, peer-to-peer (P2P) multicast live video streaming with virtual pan/tilt/zoom functionality. In this application, each user can watch arbitrary regions of a high-spatial-resolution scene yet the system exploits overlapping interests by building multicast trees. Experimental results indicate that optimal server bandwidth allocation enhances the delivered quality across the peer population.

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.

This paper proposes a scheme called Systematic Lossy Error Protection (SLEP) for robust transmission of video signals over packet erasure channels. The systematic portion of the transmission consists of a conventionally encoded video bit stream which is transmitted without channel coding. An additional bit stream generated by Wyner–Ziv encoding of the video signal is transmitted for error resilience. In the event of packet loss, this supplementary bit stream is decoded and allows the recovery of a coarsely quantized video signal, which is displayed in lieu of the lost portions of the primary video signal. The quantization mismatch results in a small, controlled loss in picture quality, but a drastic reduction in picture quality is avoided. An implementation of the SLEP system using the state-of-the-art H.264/AVC standard codec is described. Specifically, H.264/AVC redundant slices are used in conjunction with Reed–Solomon coding to generate the Wyner–Ziv bit stream. The received video quality is modeled as a function of the bit rates of the primary and redundant descriptions and the error resilience bit rate. The model is used to optimize the video quality delivered by SLEP. Via theoretical analysis and experimental simulation, it is shown that SLEP provides a flexible tradeoff between error resilience and decoded picture quality. By allowing the quality to degrade gracefully over a wider range of packet loss rates, SLEP mitigates the precipitous drop in picture quality suffered by traditional FEC-based systems.

This paper proposes a scheme for low-delay robust transmission of video signals over packet erasure channels. In applications such as video conferencing, the permissible delay between encoding and playback may be too low to allow retransmission or channel coding approaches which require buffering several video packets. For such a scenario, we present a scheme that provides error robustness using redundant video descriptions applied to pertinent portions of the video signal. In the H.264/AVC specification, this can be efficiently implemented using redundant slices and flexible macroblock ordering (FMO). We describe a model that determines the bit rate of the redundant descriptions such that the expected distortion at the decoder is minimized. Across all the video test sequences used, the average video quality delivered by the proposed scheme is 3.7 dB higher than decoder-based error concealment, and 1.2 dB higher than encoder-based loss-aware rate-distortion optimization.

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.

The novel H.264/AVC video coding specification provides a significant improvement in terms of coding efficiency compared to previous standards. In certain streaming scenarios, the problem of whole-frame loss concealment can arise when using H.264/AVC. Two different algorithms have been proposed to conceal a lost image, based on the optical flow concept. In a real streaming scenario, an encoder usually introduces some kind of intra refresh policy that can insert trouble concealment algorithms leaving gaps in the motion vector field used for reference. We discuss the advantages of introducing a motion vector estimator for such intra coded regions.

The H.264/AVC video coding standard [Joint Video Team, 2003] offers a high coding efficiency and is the first standard that provides an explicit support for the transmission of multimedia content over a packet switched network, specifying a network abstraction layer (NAL). If we consider the transmission of a low resolution video sequence over a wireless LAN network, we can usually observe that a coded frame typically fits the packet size, therefore a transmission error usually produces the loss of a NAL unit and hence of a whole frame. In this paper we propose a low complexity algorithm useful for the concealment of a whole frame, based upon the optical flow concept.