In this article we analyze scalable video transmission, from the perspective of video coding standards and the necessary developments in protocols that support media distribution in current and future network architectures. In the next section we start by describing the first contributions to this topic and following developments in related video coding standards. We then describe the structure of a scalable video bitstream, taking the novel H.264/SVC standard as reference, and we further proceed with an analysis of the protocols that can be used for the description, signaling, and transport of scalable video. We describe different network scenarios and examples where scalable video offers significant advantages, before moving on to some remarks on future trends in this area, discussing those mechanisms that must be associated with SVC techniques to achieve an efficient and robust transmission system, and concluding the article.
The use of layered video transmission in IP multicast was originally proposed by Deering (1993), who suggested the transport of different video layers in different multicast groups. With this solution the encoder would produce a set of interdependent layers (one base layer and one or more enhancement layers), and the receiver, starting with a base layer, could adapt his quality by joining and leaving multicast trees, each one carrying a different quality layer.
Deering’s proposal was followed by several protocols like: receiver driven layered multicast (RLM) protocol (McCanne, Jacobson, & Vetterli, 1996), layered video multicast with retransmission (LVMR) protocol (Li, Paul, Pancha, & Ammar, 1997; Li, Paul, & Ammar, 1998), and ThinStreams (Wu, Sharma, & Smith, 1997).
The advantages of layered video multicast were confirmed by Kim and Ammar (2001) for scenarios where receivers are distributed in the same domain, with multiple streams sharing the same bottleneck link, as occurs in many video distribution scenarios.
Key Terms in this Chapter
Unicast: Process of transmitting a flow of data from a source to a particular receiver.
IP Multicast: The transmission of Internet protocol (IP) datagrams from a source to all the receivers that belong to a certain IP multicast group. In IP multicast, terminals that wish to receive data must register with that multicast group. IP multicast routing protocols are used to create distribution trees.
Quality of Service (QoS): Process of providing different priorities to different flows of data or to guarantee a certain level of quality to a data flow. Examples of quality parameters are transmission rate, delay, delay variation (jitter), and packet loss.
Automatic Repeat Request (ARQ): A method for error control in packets or frames that uses redundant bits, acknowledgment packets, and timeouts to detect and retransmit data affected by errors.
Forward Error Correction (FEC): A method for error correction that uses redundant bits to detect and correct errors in data without the need for retransmission.
Transcoding: The process of partially or totally decoding and re-encoding a certain video stream in order to change its characteristics in terms of definition, frame rate, or transmission rate.
Broadcast: Process of transmitting a flow of data from a source to all receivers of the broadcast domain or of the network where the terminal operates.
Simulcast: Also referred to as replicated streaming, the process of simultaneously encoding and transmitting a same video sequence through a discrete number of quality video streams to several receivers.
Network Adaptation Layer (NAL): An H.264 syntax structure that represents a frame or part of it, integrating information about its encoding parameters. NAL structures are appropriate for the transport of H.264 over several types of networks.