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stream. If the amount of available bandwidth decreases more, the server degrades video quality further, until only the audio is left. This ensures that the clip can be followed even during excessive congestion. Version 9 added several enhancements to the servers including a fast-start, thus avoiding the usual long buffering before a stream starts to play. The latest free downloads, as well as more information, are available at Microsoft s Windows Media web site and through the Microsoft Developers Network. Summary The development of the streaming file format and the associated streaming server were the original drivers for the technology. Sophisticated compression algorithms have enabled transmission of video and audio over very modest bandwidths. The Internet is the ubiquitous glue that connects the far corners of the world, so that we can send the video and audio long distances without resorting to the expensive medium of television, affordable only for mass market programming. One of the drawbacks often cited for HTML is the need to design pages that render effectively with different browsers. Although the experienced web designer will get to know all the tricks, there are many pitfalls for the novice. The end result is the many unpredictable page views that we encounter by chance across the Internet. Unfortunately, streaming media has perpetuated this rather chaotic position, with the coexistence of a number of proprietary architectures. Although there are ways around this that involve authoring in a number of formats, the problem is exacerbated if you want to use interactive rich media. The three proprietary architectures do not have exactly complementary feature-sets, although there is a gradual move toward the MPEG-4 standards. Audio and video communications have developed throughout the twentieth century. From film to television to IP streaming, system developers have striven to deliver the optimum quality that the channel will support at a reasonable cost to the consumer. The twenty-first century promises to offer new business opportunities for content owners to exploit not only the Web, but wireless and broadband delivery channels. The MPEG-4 team has embraced these new channels. From use of the Web, CD-ROMs, and DVDs, consumers expect interactivity. Other sectors, especially games developers, have shown how virtual reality can contribute to entertainment. MPEG-4 embraces this concept, along with graphics and synthetic audio, to offer a new platform for the authoring of creative and compelling content. Although the early applications of MPEG-4 have been as a conveyor of a rec- 152 The Technology of Video and Audio Streaming

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switch between versions to deliver the highest-quality stream that the viewer s connection can support at any given time. This real-time switching effectively handles changing network conditions, such as congestion. Switching of audio and video is handled independently, and you can indicate whether the video or audio should be given preference as the viewer s throughput drops. In addition to the SureStream feature, the RealPlayer can also drop frames and/or degrade the image quality to maintain real-time playback over slower connections. If the available bandwidth drops very low, the RealPlayer can omit the video track entirely and simply play the audio track. See Real and RealNetworks web sites for comprehensive background information. Windows Media Windows Media 9 Series is Microsoft s complete solution for delivery of Internet multimedia. The architecture includes a number of products for encoding, serving and distribution, and an integrated and fully featured rights management system. An SDK allows integration into wider systems. Although the main product line is available only on the Windows operating system, Microsoft has a player for Mac OS X, and embedded players for consumer devices from DVDs to portable music players. Windows Media 9 has applications beyond streaming to PCs, and also can be used for the delivery and distribution of high definition television with high-quality surround sound. DVD players and set-top boxes are beginning to offer support for these new facilities. The Windows Media tools include the Windows Media 9 encoder and Windows Media Services for control and configuration of the media server. This supports both live and on-demand video, and forms part of the Windows Server 2003 product. This potentially can offer a low-cost media and web server solution. The Windows Media rights management allows content creators to set up a full e-commerce system to sell or rent streamed content. It also can be used for delivery of confidential media clips. The initial releases of rights management supported pre-encoded content. With version 9, Microsoft introduced DRM support for live content. Scalability Windows Media Server offers scaling of the transmitted data rate through the use of multiple video tracks, called intelligent streaming. At the beginning of playback, the Media Player and the Windows Media Server negotiate to select the video track that best matches the viewer s connection. If the network s performance degenerates, the server automatically sends a lower rate video Introduction to streaming media 151

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Scalability QuickTime offers multiple bit rate delivery through its alternate movies feature. At the beginning of playback, the QuickTime Plug-In requests an alternate version according to the settings the viewer has configured in their QuickTime Settings control panel. Content creators may create as many alternates as they need when they are encoding the movie, and specify complex criteria for when particular versions will be displayed. This allows for delivery of content based on bandwidth of the user s connection, playback platform (Mac or Windows), Quick- Time version and language (to select different audio tracks), or the CPU speed. QuickTime can be served from the Mac OS X server or the open-source Darwin server. The QuickTime Pro can be used for authoring, with the Quick- Time Broadcaster product adding facilities for live streaming. RealNetworks RealNetworks pioneered streaming as a usable communication medium under the name Progressive Networks. Before the Real player, audio-visual content was delivered as a download, to be played later from the local drive. The Real 10 platform, incorporating RealAudio and RealVideo, is a networkoriented, streaming media architecture developed by RealNetworks. Real 10 provides further improvements in quality, supported media types, and features over earlier versions. Real 10 is a streaming architecture, offering both server-based true streaming and serverless HTTP streaming (also known as progressive download). There are performance and scalability advantages with the server, but you can get started without one. High volume sites, however, definitely need a server for improved delivery performance. Real 10 is most appropriate for network delivery of audio, video, and other media types, such as text and Flash animations. Users can view Real 10 movies with the RealPlayer 10 (Real One), a free client application available from RealNetworks. The enhanced RealOne Super- Pass provides additional features, and must be purchased from RealNetworks. Real 10 supports Synchronized Multimedia Integration Language (SMIL, pronounced smile). This language enables the content creator to synchronize media and actions within a web page to the video and audio tracks. For example, SMIL can control the loading of multiple movies at given times, URL page flips, transitions, text tracks, and advertisement insertion. Scalability Real 10 offers dynamic stream switching called SureStream. During playback, the RealPlayer and RealServer continually communicate and can repeatedly 150 The Technology of Video and Audio Streaming

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local node. If everyone on the block tries to watch high-bandwidth streams simultaneously the contention for the available bandwidth will cause degradation of the streams. DSL, much like the analog modem, will be limited by line conditions. The rule is always to encode at a lower rate than the maximum the circuit is specified to carry. If you are using standard encoding tools these will have headroom already built into the encoding templates. Proprietary codec architectures There are three popular codec architectures: Apple QuickTime, Microsoft s Windows Media, and RealNetworks. Each product supports a number of different compression codecs, although there is more choice of audio versus video codecs. Apple QuickTime QuickTime is Apple s multi-platform, multimedia software architecture. It originally was used by content creators to author and publish CD-ROMs. It also offers virtual reality with 3-D views of objects and panoramas. The initial support for IP delivery was by progressive download. It was extended to support true streaming in version 4, utilizing the RTSP framework. QuickTime 6 expands support for international standards, MPEG-4, and for third-generation wireless applications 3GPP and 3GPP2. Because QuickTime has an established position in multimedia authoring there is a large community of users. Some of QuickTime s features include the following: Multiple delivery channels: WWW, CD-ROM, DVD, wireless broadband, kiosk, presentations Players for Mac and Windows Powerful interactive capabilities Synchronized graphics, sound, video, text, music, VR, and 3-D for rich media production QuickTime is the dominant architecture for CD-ROM video. It enjoys an impressive market share due to its cross-platform support, a wide range of features, and free licensing. For these reasons QuickTime is used on the vast majority of CD-ROM titles. The MPEG-4 team adopted the QuickTime stream serving methodology (with the use of a hint track and RTSP/RTP) as the basis of MPEG-4 streaming. Introduction to streaming media 149

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148 The Technology of Video and Audio Streaming streaming media 28K modem Audio CD DVD video DV studio interconnections T-1 1.5 Mbits/ 270 Mbit/s 2.8 Mbit/s 30 kbit/s to 1 Mbit/s average rate 4.7 MBit/s uncompressed standard-definition uncompressed stereo Media Stream rate Notes 25 Mbit/s < 10.7 Mbit/s Figure 7.8 Media bandwidths. Table 7.1 Typical Carriers for Delivery of Streaming Maximum Actual Notes Dial-up modem 56 kbit/s 35 kbit/s Dual ISDN 128 kbit/s 128 kbit/s Cable modem/DSL 1 8 Mbit/s 300 kbit/s 2 Mbit/s Rate varies with supplier T-1 1.5 Mbit/s 1.5 Mbit/s 10 base-T LAN 10 Mbit/s 3 Mbit/s Typical

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Bandwidth, bits, and bytes The units bit and byte occur throughout this book. Although you know that a byte is 8 bits, it is very easy to get the two mixed up. Most of this stems from the abbreviations: B = byte b = bit To avoid confusion it is always best to spell out the abbreviations in full. Have you ever purchased eight times more disk storage than you needed because b and B were swapped around? Alternatively, midway through a live webcast the disk archive is completely filled. In general, bits refer to streams and bytes to memory and storage. So a 10-second clip at 80 Kbit/s (that is, 10 Kbyte/s) needs 100 Kbytes of storage. The other point is that although the standard multiplier of kilo-means 1,000, in the computer industry it represents 1,024 (or 210). The two are abbreviated to k and K, respectively. If they are mixed up the error is going to be only 2 percent. 1 byte = 8 bits 1 kbit = 1,000 bits 1 Kbit = 1,024 bits Bandwidths and file sizes Streaming is very different from other media in the sheer range of bandwidths that can possibly be encoded. Whereas television is essentially a fixed bandwidth (although the bit rate can vary within close limits), streaming may be delivered down anything from an analog phone line to a high-speed local area network, or 28 kbit/s to 2 Mbit/s or higher. The starting point for uncompressed audio is a bit rate of nearly 3 Mbit/s from a CD. For video the studio interconnection standard is 270 Mbit/s. The compression used with DV camcorders has a video data rate of 25 Mbit/s (although it can be transferred at different rates over the IEEE 1394 interface). The streaming media has to be compressed to match the capacity of the user s connection. These vary widely; an analog modem will have a maximum rate of 56 kbit/s, although many users still use 28 k or 14 k modems (although the latter are not adequate for video streaming). Most connections quote a maximum rate, but usually this is not achieved, except for ISDN and T-1, where the data rate is guaranteed. The dial-up modem will be limited by propagation conditions on the line, factors like noise pickup. The cable modem uses a shared fiber back to the head-end from your Introduction to streaming media 147

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146 The Technology of Video and Audio Streaming media player personal computer personal computer download folder hard drive video & audio from network video & audio from network Streaming Download-and-play media player Figure 7.7 Download-and-play and the streaming player.

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Distribution In principle, the distribution is simple. As long as there is IP connectivity between the server and the player/client, the requested packets arrive at the player. In practice, it is not that easy. No doubt you have seen a stalled media file; the video is distorted and blocky, the audio has silent passages. The problem is that the Internet was not originally designed to support continuous streams over persistent connections. It is basically a packet-switched system for asynchronous data. Several different developments are aiding improvements to the delivery quality. First is increased bandwidth for the last mile to the consumer. Through either the cable modem or DSL, downloads of 1 Mbit/s or higher can be achieved. The next development is the content delivery network (CDN). These use a smart overlay on the Internet to provide content-aware routing. The final development is the quality of the Internet. More and more fiber is installed, and QoS protocols help differentiate priority traffic. The catch is that as quality improves, more companies will use streaming. This creates more traffic and potential congestion the race that never ends. Player A regular web browser can render text and images only in JPEG, PNG, and GIF formats. A special media player is required to render streaming files. Players are usually supplied as free downloads, or are pre-installed with the operating system. Some vendors also have a fully featured player available for a small charge. Plug-in, player, or portal The player can be used as a plug-in to a web browser. The alternative is to use a stand-alone player. These players have been developed into media portals, with navigation to popular material, and often offering unique content specific to a given architecture. Download versus streaming Download-and-play is what it says: The file is downloaded to the local hard drive, and once the entire file has been delivered, the viewer can play the file locally. In contrast, streaming is processed chunk by chunk as it arrives, and is rendered directly to the display; then the data is discarded. So there is no waiting; if you do not like what you see you can quit the stream immediately, rather than downloading the entire file before you decide. Note that there is no local copy of the file stored on the hard drive. This greatly aids in the protection of content from illegal copying, although it is not foolproof against the determined hacker. Introduction to streaming media 145

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On-demand and interactivity One major delineator of streaming from regular television is the interactivity. The viewer can interact with on-demand content files. The player has VCR-like controls (PLAY, STOP, FF, REW) and random access to any part of the clip. Hotspots on the video screen can take the viewer to another part of the file, or to a different file, at the click of a mouse hypervideo replaces hypertext. To support this functionality a special streaming server is used rather than a regular web server. The streaming file is time indexed to enable the random access. This means that a long program can be split into chapters with random access by the viewer to any chapter at will. 144 The Technology of Video and Audio Streaming Internet Media player Streaming server live production stream stream stream Media player Content server Streaming server production upload stream stream request clip upload Live streaming On-demand streaming Internet Figure 7.6 Live and on-demand.

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A special case of live streaming is simulated-live, where the content is delivered by a server-side request. This can be mixed at will with a live presentation. So a speaker could be introduced with a promo, speak live to camera, and then show a prerecorded clip from the server. Streaming requires a persistent client-to-server connection and continuous data flow. Contrast this with the burst transmissions of a web server connection. Introduction to streaming media 143 2 x B bit/s B bit/s data rate X bytes media file media file ‘X’ bytes X bytes T 2 x T download time Download Streaming media file variable rate channel, fixed data-rate stream data rate control Figure 7.5 Download versus streaming.

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