Video Compression Algorithms and Related Transport Protocols for Real Time, Unicast and Multicast Video over internet

支持互联网上的低延迟视频通信是一项重要而又具有挑战性的任务。一些可能的应用包括视频会议、远程医疗和交互访问存储在远程数据库中的预先录制的视频。网络视频通信有两个主要要求：(1)带宽可伸缩性；(2)容错性。缺乏带宽可伸缩性导致非自适应流具有两组缺点。首先，当视频流量的总带宽超过网络容量时，它会导致拥塞崩溃。其次，它与其他自适应流量不公平地竞争，如TCP，在网络拥塞的情况下降低了传输速率。缺乏差错恢复能力会导致差错传播，从而导致视频质量随时间变化很大。当前减轻差错传播影响的方法包括传输层的差错控制机制。这通常采取重传或前向纠错(FEC)的形式。基于重传的差错控制方法往往不是实时的，特别是在往返传播延迟较大的情况下。另一方面，前向纠错方案在突发丢失时往往是无效的。该方案的主要目的是研究在尽力而为的网络(如因特网)上实时传输单播和多播视频所需的视频压缩技术和传输协议。对于单播情况，我们的方法是将一种新的具有容错性和带宽可伸缩性的压缩方法与低延迟的TCP友好传输协议相结合。具体地说，压缩视频被打包成具有相同预期视觉重要性的可单独解码的分组。因此，在有损条件下，可以在接收器处实现相对稳定的视频质量。此外，分组可以被截断以即时满足由TCP友好的传输协议施加的时变带宽。结果，产生了对其他互联网流量友好的自适应流。通过实际的互联网实验和仿真，对压缩、传输和组合方案的性能进行了评估。我们的组播视频传输方法是将带宽可伸缩的视频压缩方案与分层前向纠错编码相结合。所谓分层FEC，我们指的是产生嵌入的FEC或冗余流，每个流属于不同的组播组。这样，订阅更多的组对应于更高的保护级别，但延迟更大。这种方法有两个优点。首先，每个接收器可以根据过去的接收统计数据和损耗特性独立地调整所需的保护级别。这种接收器驱动的FEC方法比大多数现有的用于多播的FEC方案更灵活，其中源确定一组冗余分组，然后将这些冗余分组多播到每个接收器。其次，每个接收器将只订阅所需数量的冗余层，从而降低整体带宽利用率。此外，FEC层的分层性质确保了通过共享公共冗余流将网络利用率降至最低。将进行实际的互联网实验，以检验我们方法的有效性。

Supporting low latency video communication over the Internet is an important yet challenging task. A few possible applications include video conferencing, tele-medicine, and interactive access to pre-recorded videos stored in remote databases. There are two main requirements for internet video communication: (1) bandwidth scalability; (2) error-resilient. Lack of bandwidth scalability results in non-adaptive streams with two sets of disadvantages. First, it leads to congestion collapse when the aggregate bandwidthof the video traffic exceeds network capacity. Second, it competes unfairly with other adaptive traffic, such as TCP, which reduces transmission rate in face of network congestion. Lack of error resilience results in error propagation, and hence widely varying video quality as a function of time. Current approaches to mitigate the effects of error propagation include error control mechanisms at the transport level. This typically takes the form of retransmissions or forward error correction (FEC). Retransmission based error control methods often fail to be real-time, particularly when round-trip propagation delay is large.FEC schemes on the other hand, are often ineffective when losses are bursty.The main goal of this proposal is to investigate video compression techniques and transport protocols needed for real time delivery of unicast and multicast video over best effort networks such as the internet. Our approach for the unicast case is to combine a novel compression method that is error resilient and bandwidth scalable with a low-delay TCP-friendly transport protocol. Specifically, compressed video is packetized into individually decodable packets of equal expected visual importance. Consequently, relatively constant video quality can be achieved at the receiver under lossy conditions. Furthermore, the packets can be truncated to instantaneously meet the time varying bandwidth imposed by a TCP-friendly transport protocol. As a result,adaptive flows that are friendly to other Internet traffic are produced. Actual Internet experiments together with simulations are used to evaluate the performance of the compression, transport, and the combined schemes.Our approach to multicast video transmission is to combine bandwidth scalable video compression scheme with hierarchical FEC. By hierarchical FEC, we mean the production of embedded FEC or redundancystreams, each of which belongs to a different multicast group. This way, subscribing to more groups corresponds to higher level of protection, but larger delays. There are two advantages to this approach. First, each receiver can independently adjust the desired level of protection based on past reception statistics and loss characteristics. This receiver-driven approach to FEC is more flexible than most existing FEC schemes for multicast where the source determines a set of redundancy packets which are then multicast to every recipient. Second, each receiver will subscribe to only as many redundancy layers as necessary, reducing overall bandwidth utilization. Furthermore, the hierarchical nature of the FEC layers ensuresminimum network utilization through sharing of common redundancy streams. Actual internet experiments will be done to examine the effectiveness of our approach.