to offer short clips by download and play, but streaming also can be used. Content can be encoded using MPEG-4 codecs, or can use proprietary codecs like Oplayo. This uses a lightweight player that can run on Java and Symbian platforms. The Oplayo technology also can run on GPRS network, so allowed service providers to offer video services prior to 3G network availability. The minimum bandwidth requirement is 10 kbit/s and it integrates with standard WAP and Web servers. One advantage of the cell phone is the existing systems for billing for premium services. An equivalent did not exist for delivery to the desktop PCs via the Web. Applications for streaming media 313 Figure 16.2 Oplayer media player for mobile applications from Oplayo.
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Typical presentations combine streaming media, PowerPoint slides, text transcripts, and interactive facilities like web chats. Training Streaming adds a new dimension to distance learning. The learner now can see and hear the lecturer, and interact with forums and chats. The same technology also can be used with corporate networks and the metropolitan area networks used by college campuses. Most training solutions employ the conventional synchronized rich media model, often backed with linked documents in PDF format for background reading. The tools for creating content have become easier to use and lower in cost than initial product offerings. Training can be a live webcast, or lectures called up on demand from an archive. The learner now can be separated in time or space from the lecturer, yet still feel the bond of the video communication. Traditional text-based distance learning was plagued with high drop-out rates. The addition of audio and video adds immeasurably to the bonds of communication. Entertainment The streaming of legally obtained entertainment has had a slow start. The content providers have to see a return. The poor quality of early distribution networks meant that the public was unwilling to pay plus they could get content from peer-to-peer networks, albeit by the theft of intellectual property. The advent of DRM and better content delivery networks means that content owners now are prepared to sell content via the Internet. Internet radio The webcasting of audio began in 1993 with Internet Talk Radio. It is now possible to listen to thousands of streamed radio stations from all around the globe. All genres are covered, and the technology has reached maturity. The bandwidth demands are reasonable compared with video streaming, and the audio quality can be very good. Mobile As third generation (3G) cellular wireless networks roll out their coverage, it has become feasible to deliver video to mobile devices. Early services have chosen 312 The Technology of Video and Audio Streaming
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They use a combination of video and graphics that has been developed over a period of 50 years to produce content that is compelling to follow and easy to understand. You will notice that there is a strict limit on the amount of information presented. A television program rarely will convey more than six key facts in 30 minutes, a long time for a webcast. The graphics are kept simple. As web developers have discovered, people will not read vast amounts of text on a screen. Often they graze the text, linking rapidly from one page to another. The next point is to deliver a good quality image; that means restricting the aggregate data rate to sensible levels. The well-known saying is that the viewer will not wait. After a few seconds waiting for a download most viewers will click away to another site. Another rule gained from the CD-ROM is to make it interesting by involving the viewer. Interactivity is the answer here. To reinforce the experience, make it immersive. Applications for streaming media 311 Lorem ipsum Dolor sit amet Consectetaur Adipisicing elit Ut labore et dolore Lorem ipsum Dolor sit amet Consectetaur Adipisicing elit Ut labore et dolore E ercitation Eu fugiat nulla Pariatur John Doe: Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Jake North: Et harumd dereud facilis est er expedit distinct. 75 Kbps 00:12:06 Streaming Media Video Audio PowerPoint Slide presentation Audience interaction web chat Slide navigation slide titles HTML page Figure 16.1 Typical elements of a rich media web page.
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activity. Basic support uses the binary format for scenes (BIFS), which provides interaction between scene objects. JavaScript and Java provide more sophisticated functionality. Applications for streaming include: Training Entertainment (Internet radio and VOD) Corporate communications Marketing Advertising Some applications use streaming as the primary focus, others use streaming as a tool. A typical example of the latter is the use of streaming media as a proxy for broadcast quality content in digital asset management systems. Another use is for the rapid approval of clips, often needed when making commercials. The video production industry needs to exchange dailies (rushes) of clips to interested parties to preview the production processes. These parties could be in another city or even another continent. For such applications streaming media is an ideal vehicle. Rich media Rich media used to be the preserve of the CD-ROM. Tools like QuickTime allowed a combination of text, graphics, and video to be combined into an interactive presentation. In contrast, web content was limited to text and still images. The later development of Flash allowed content creators to enliven their static web pages with compelling vector graphics. Streaming media now allows regular video to be added to web pages, so the same mix of formats that was once restricted to the CD-ROM now can be delivered in real-time as a stream. Before embarking on a rich media project, it s best to sit back and think, What and how am I trying to communicate? If you want to webcast, use it because of its strengths; if you are using it as a substitute for a different medium your results may be less than optimum. Above all, it must hold the attention of the audience. That dictates the maintenance of high production values. Whatever the codec designers may claim for video quality, the results can be less than satisfying once the stream has been distributed over the Internet. If you want the viewer to enjoy the experience, you should always plan the content for worst-case delivery quality, possibly offering alternative streams for narrowand broadband users. Many examples of rich media have indicated a complete lack of appreciation of the experience gained by the producers from other media formats. Some of the results of best communicators can be seen in regular television programs. 310 The Technology of Video and Audio Streaming
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16 Applications for streaming media Introduction In a period of ten years, streaming has evolved to become a primary medium for the delivery of video and audio content. It sits beside television for use in applications where the audience is too small or dispersed to warrant conventional broadcasting. Other communications media now are finding that the codecs developed for Internet streaming have many other applications. Streaming demands highly efficient compression for the limited bandwidth available. These efficient codecs also can be used to reduce very high data rates high-definition television or for the very low data rates of mobile wireless applications. We see MPEG- 4 and Windows Media being adopted for high-definition DVD coding, and MPEG-4 forms a key part of third-generation wireless standards. This chapter explores some of the applications of streaming. Although streaming can be used standalone to deliver audio and video content, it is often deployed as a component in a wider system often called rich media. The advent of SMIL (Synchronized Multimedia Integration Language), has given content producers the tools to seamlessly assemble video, audio, animated vector graphics, and stills into the compelling and interactive experience that is rich media. At a simple level, one of the most-used styles is a combination of PowerPoint slides with accompanying audio and video. Such multimedia presentations can be used for sales promotions, distance learning, and product launches. It adds another component to the marketing mix, one that has the immediacy of video and the interactivity of the CD-ROM. MPEG-4 offers new ways to create interactive applications, with features previously found in the DVD and CD-ROM. MPEG-4 was conceived to support object-based interactivity. Objects are not just video and audio, but many different types of content including 2- and 3D objects, animation, graphics, and text. The many objects are all delivered as parts of the stream. The viewer can use hotspots on the screen to switch objects at will; alternately, one object can trigger another object. MPEG-4 supports both client-side and server-side inter-
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Edge serving by CDNs has been very successfully applied to static web content. To extend this to streaming is not trivial; the demands for disk space at the caches are large, but disk prices are always falling. The method can be applied successfully within a closed system, where a sensible booking system can be used for space. This could be a corporate network or a campus-wide system. On the public Internet it is possible for special events with very large audiences to use caching effectively. The alternative is a hybrid approach a prefix of the media clip could be cached to give a rapid start to the stream. The remainder of the stream then is pulled from the origin to the edge. The CDNs are content-aware and can apply smart routing algorithms to avoid traffic bottlenecks in the Internet, potentially lowering packet loss and delay. A big advantage with the CDN is that a live webcast can be split at the POP. This replaces a stream per client with a single stream from the origin server. The final goal would be the ability to multicast across disparate networks; this offers the best potential to reduce network congestion for live webcasts. The on-demand user is a more difficult customer to satisfy with high-quality delivery. If content is little used there is no advantage in caching; there are going to be different standards for popular content, which possibly could be dispersed to the edge, and content that is used very occasionally. To expect otherwise would need a CDN with a capacity that would not make economic sense. When selecting a CDN to deliver to the public, size counts. If the CDN owns the fiber, has control over as much of the routing as possible, and has edge caches, then the stream is going to arrive in better shape than if it is launched into an unknown number of peered networks before arriving at the viewer s ISP. As the bottlenecks are removed and the performance of streaming improves, more companies will want to use rich media, so the traffic will grow and congestion will increase. The improvements will have to continue at a pace to keep up with ever-increasing demand; it is just like building a highway network traffic expands to meet the capacity and is regulated only by congestion. 308 The Technology of Video and Audio Streaming
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VSAT The use of very small aperture terminals has revolutionized satellite communications. The 4 5 meter diameter dishes common with C-band have been supplanted with compact Ku-band antennae, less than 1 meter in diameter. Typical capacities of a geo-stationary satellite (in the year 2000) were in the region of 108 Mbit/s of bandwidth per cell. A cell is about 640 km in diameter. Hughes Network Systems have a system called DirecWay. This satellite distribution offers several advantages for the multicasting of live events. Only one stream is sent up to the satellite, and then any authorized user within the antenna footprint can participate in the webcast. The Ka-band now is being used in the search for more free space in the RF spectrum. This band uses a compact dish with small beam width, but does suffer attenuation if there is rain in the path of the beam. Summary A compelling viewing experience demands a media stream that does not stall, that does not lose the audio. To achieve this goal, the bottlenecks that slow down the data packets have to be eliminated. As a clip is transferred from a live encoder or an origin server, the first impediment may be the link to the backbone. This is often a problem for live webcasts. The capacity of the available existing circuits may not be sufficient. Satellite back-haul may be an option. The next step is to cross the backbone. Improvement in capacity has been assisted by the ever-increasing bandwidth of the fiber backbones, but the capacity of the last mile has not kept pace. Many incumbent utilities are burdened with an historic infrastructure designed for the plain old telephone service. The investment required to bring fiber to the curb is staggering, with a long payback time. This is an area where the television broadcaster wins hands down. They have a fixed cost for transmission. It makes no difference if there are a hundred or a million receivers within range of the tower. Even if the end-to-end connection could be established satisfactorily, it is unlikely that all the remaining components are going to have excess capacity. Traffic always expands to fill the excess. So how can the traffic cross the Internet without suffering delays? Content Delivery Networks (CDNs) mean that files no longer have to be served right across the Internet. Instead, content is delivered from servers placed at the edge of the Internet in your local point-of-presence. This edge serving makes for a much better viewing experience, without all the problems that packet loss and delays can cause as clips transit the Internet routers. Content distribution 307
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can improve the streaming experience, without requiring a complete swap-out of the network infrastructure. Diffserv can assign packet priorities, MPLS allows control over traffic, and RSVP can reserve resources at the edge. None of these protocols can make bandwidth available if the network is overloaded, so they are not a substitute for proper traffic engineering. Satellite delivery Some people are looking up to the sky for the answer to Internet congestion. Satellite communication can be used in two ways. One is to supplement the Internet backbone; the other is for direct connection to the user. Satellites are particularly useful for handling peak demands for popular webcasts. The satellite hops can completely bypass the backbone, by streaming multicasts to the edge of the Web. The Internet can be used for the back-channel to gather usage statistics and manage authorizations. The main bandwidth-hungry content data travels via the satellite circuit. Multicast Satellites are an efficient way to distribute multicasts to widely dispersed audiences. Any POP within the footprint of the downlink potentially can receive a multicast feed, without all the intermediate routers that a fiber connection would entail. Satellite to the user So what about the person who has had enough of the city and heads for a cabin in the hills? Technologies like ADSL are limited to a range of about 5,000 meters from the central office. One solution for remote sites is to use satellite delivery of broadband content. Satellites are also a good way to multicast a single stream to large audiences. They do not have the capacity for on-demand streaming to the very large numbers that the terrestrial circuit can offer, but are more suited to the burst transmissions of general web page downloads, where many users can share the same bandwidth. Satellite can be one-way or two-way. One-way uses a regular telco backchannel, for example, through a dial-up circuit. This is an asymmetric configuration, but for the average user, the much lower bandwidth of the back-channel would be no more of an issue than that experienced by the ADSL user. Note that in some countries the regulatory authorities do not allow private uplinks, stemming from paranoia about security and state control. 306 The Technology of Video and Audio Streaming
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label switching. The IP layer of the Internet uses best-effort delivery. The complexity to ensure error-free delivery is located at the server and client using a protocol like TCP. IP works very well; it uses a simple network system. But as the traffic grows to the point of router congestion, then packets are dropped. This causes delays and jitter. This is not a problem for general data traffic, but is an issue with real-time applications like multimedia and voiceover IP. Even if you opt for a CDN, improving the intermediate network can only help. The challenge to improve the quality of service is to implement improvements without increasing complexity at the core of the network. Some technologies can be employed on closed systems like intranets, but rolling out developments to the public Internet is not as easy. RSVP Resource Reservation Protocol allows a client (the media player) to request a guaranteed network resource for unicast and multicast data flows. Resource Reservation is complex and too much of an overhead to be used generally across the Internet, but it can be deployed usefully at the edge. Potentially it delivers the best QoS delivery for packets. MPLS Multiprotocol Label Switching (MPLS) has emerged as a step on the road to photonic networks. It is used not just for IP (hence the qualifier multi-), but also other packet-switching protocols like frame relay. The label contains layer 3 routing information to indicate the next router hop. This means that the routers simply can switch the packet, using the data in the label. The data takes the label-switched path rather than using the usual router paths. This means that the labels can be assigned to allow control over the network traffic, hence providing potential routes around congestion. Diffserv Differentiated services or Diffserv allows coarse information about the service requirements of a packet to be coded in the IP header. It replaces the type-ofservice or traffic class field in the header and determines the priority within the router. Diffserv marks traffic at the input to a network and is unmarked when the packet leaves that network. To operate, Diffserv requires a service level agreement at network peering points. There is no holy grail for improving the quality of service for media streams crossing the Internet. There are a number of solutions that deployed together Content distribution 305
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low value, and a high value set for a congested Internet connection. If a backchannel exists, the receiver can request resends of corrupted packets; this can be used in combination with, or instead of, forward error correction. Improving the QoS Alongside edge serving many strides are being taken to improve the QoS of the Internet. Two initiatives are resource reservation and multiprotocol 304 The Technology of Video and Audio Streaming 2 Helix RealPlayer Gateway Helix Universal Server transmitter encoder 2 Helix Gateway Helix Universal Server encoder transmitter push initiation pull initiation satellite fiber Helix Gateway Helix Gateway redundant paths to relay transmitter forwards media stream in response to request from receiver player requests media file receiver passes on request player receives media transmitter pushes media to configured destinations Figure 15.11 Push and pull with Helix server.
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