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MillimeterNew Currents in Streaming
Sep 4, 2001 12:00 PM, Philip De Lancie
A look at where developing markets and technologies are taking IP video.
Painful as it has been for investors, the dot com dive in financial markets has been a useful reminder that doing it over the Internet – whatever “it” is – doesn’t allow you to ignore the fundamentals of your chosen field. If commerce is your game, your days are numbered unless you manage to take in more than you spend. If your field is communication, there’s another fundamental you’d best not ignore: Your medium won’t hold your audience unless it provides acceptable “quality of experience.”
Along with compelling content, a medium’s convenience, cost, and audio-visual resolution all shape the end-users’ perceptions of their experience. Today’s popular media exhibit each of these qualities in varying proportions. Broadcast television, for instance, is inexpensive, and may (depending on your local topography) provide passable audio-visual quality. But it’s not really convenient unless the content you want to watch happens to be on precisely when you want it
Video streamed over Internet Protocol networks, on the other hand, holds out the tantalizing prospect of true video on demand, with any program just a click or a remote-key away at any hour of the day. That covers convenience, but it doesn’t address the issue of audio-visual resolution. There’s a minimum threshold below which it is nearly impossible for viewers to suspend their consciousness of the medium and concentrate instead on the content. Video streamed over broadband connections (DSL, cable modem, Ethernet) may meet this critical test, but video over dialups does not.
For the foreseeable future, the vast majority of home Web users will access the Internet via dialup. That doesn’t mean that streaming video is dead on arrival. But video professionals intrigued by streaming’s potential should probably take a realistic look at where the opportunities really lie in today’s market, and also keep an eye on how developments in technology may influence the markets of tomorrow.
Today’s market
In terms of today’s streaming video market, at least two developments bear watching. The first is that more and more non-consumer Internet users – corporations and institutions – have the bandwidth for streaming, not only within their operations (intranet) but also to and from the Internet (broadband connections). This makes the corporate market the prime growth area right now for services related to video streaming.
“For now, the bandwidth is in the corporation,” says Scott Gordon, vice president of marketing at SeeItFirst in Fremont, California. “And we have seen rapid adoption of streaming video in the corporate space. The investment is based on the application’s cost-benefit. Applications include webcasting large corporate events, training internal personnel, informing shareholders, training sales partners, extending customer service and support, launching products, and enhancing human resource initiatives. It’s basically about efficiently disseminating important and timely information in a captivating and interactive medium.”
Another important trend is that broadband to the home, while still a small piece of the pie, is growing rapidly. The audience size required to make entertainment-oriented video streaming a viable proposition may be a ways off, but it is coming.
“Don’t let the current number of broadband-enabled consumers hide the underlying trend,” says Greg Lowitz, general manager of the Webcasting Solutions Group at Pinnacle Systems in Mountain View, Calif. “The demand is there, but the companies providing the service are working through the issues that face any start-up business or industry as it scales to meet that demand. The fact is, consumers want broadband faster than telcos and cable companies have been able to roll trucks to the home.”
Scaling redefined
Even as deployment of broadband expands, millions of users will continue to access the Internet via dialup, and adoption of low-bandwidth wireless devices will continue to grow. That means the demand for ever more efficient ways to utilize existing bandwidth will continue. Compression is key, of course, and we can expect further advancements in the existing codecs used in RealVideo, QuickTime, and Windows Media. But it seems unlikely that these codecs alone can ever make low-bandwidth video truly palatable. Instead, performance will advance through a combination of technologies, some existing and some new.
One key development will be a redefinition of the concept of scalability, enabled by the MPEG-4 standard. A comprehensive description of the standard, which is designed to facilitate the streaming of a wide variety of media content at bit-rates ranging from next to nothing up to 10Mb per second, is beyond the scope of this article. But with MPEG-4, it becomes possible to move beyond the simple “bandwidth negotiation” of today’s media players, in which the server determines the bandwidth of the connection and delivers a stream that has been pre-made to match one of a few common bit-rates.
MPEG-4’s scalability operates simultaneously at several different levels, and on several different parameters. To understand it, you first have to know that MPEG-4 – like QuickTime, on which the file structure is based – was conceived to allow the integration of multiple synchronized media streams into a unified “container” format. The streams may be visual (video, animation, etc.) or aural (digital audio, synthesized music, or speech, etc.). These individual streams, along with associated metadata about their time-base, duration, etc., become “media objects.” The overall MPEG-4 file of which these objects are a part is not itself actually streamed.
Another key MPEG-4 concept is that the exact presentation transmitted to and experienced by a given end-user is both context-dependent and interactive. Media objects maintain their individuality within the MPEG-4 container. The way the objects are combined at playback is defined by “scene descriptions” that use a format based in part on Virtual Reality Modeling Language (VRML). These descriptions can be conditional, meaning that the composition of a scene may depend on the playback context, including both the connection over which the scene is transmitted and the device on which it is played.
At the scene level, MPEG-4’s scalability means that the number of objects used to compose a scene may vary depending on bandwidth. Rather than trying to cram everything through the pipe at once, the component parts of a scene may be intelligently prioritized based on how essential they are for conveying meaning.
A news show scene, for instance, may be composed of an announcer shot against blue-screen, the announcer’s voice, a motion background (the busy newsroom), an inset video window for news footage, a character-generated headline strip across the bottom, and a background music bed. A viewer watching a television hooked to a digital set-top box might see and hear all of these objects. Over a 100Kbps connection to a PC, perhaps just the news footage would be transmitted, along with the announcer’s voice. The wireless phone user, meanwhile, would get only the announcer’s voice.
In addition to this scene-based scaling, MPEG-4 provides for each of the individual media objects to be scaled based on a number of parameters. In spatial scalability, the screen resolutions used to display textures, images, and video objects adapt to available bandwidth. Temporal scalability changes the displayed time-base (frame rate).
Perhaps the most sophisticated is quality scalability. The encoder divides the incoming signal into multiple layers: a base-case layer that must be transmitted, and enhancement layers that may be transmitted as bandwidth allows. Each successive enhancement layer fills in detail and “richness” that progressively improves the experience as bandwidth increases.
Finally, to ensure that MPEG-4 can be affordably implemented across the spectrum of consumer and professional devices, the format incorporates complexity scalability. Essentially this means that while the best playback is obtained from a sophisticated decoder design, the format is also designed to allow use of simple decoders, while ensuring that the results are still comprehensible.
The distributed network
It’s early yet in the development of tools allowing content creators to take full advantage of MPEG-4’s innovations. Once implemented however, MPEG-4 will advance streaming by allowing a much more refined approach to making the best use of each individual connection’s bandwidth. In the meantime, a couple of other approaches to better bandwidth utilization are already available. One concept that’s received a lot of attention is distributed network architecture. According to Akamai, a leading proponent of this approach, the infrastructure of the Internet involves several inherent bottlenecks.
Describing the Internet as a “network of networks,” the company says the speed and reliability of data transfer are affected not only by the capacity of the system’s backbone networks, but also by the limited number of “peering points” at which these networks hand off data. The multiple routers and backbones through which data normally travels can cause delays and packet loss.
Akamai also describes a “first mile” bottleneck, which reflects the fact that most websites disseminate data to all users everywhere from a central location. That limits the speed with which multiple users can simultaneously access a site’s data to the bandwidth of the site’s single connection to the Internet.
Akamai’s solution to these problems is to replace centralized content serving with what the company calls “edge delivery,” in which a company’s content is “cached” on server sites spread out across multiple backbones. Branded as FreeFlow, the idea is to shorten the path taken by the data on its way to the client, thereby skirting the first mile, peering, and backbone bottlenecks. To make it work, Akamai currently operates more than 6,000 servers on more than 335 networks in 54 countries. The company uses realtime monitoring of Internet traffic flow to map the fastest route to a given end-user, and to re-route in response to congestion and network outages.
A burst of video
An alternative approach to efficient bandwidth utilization is championed by Burst.com. The company offers its Burstware products as a solution for what it says are shortcomings of the two main methods used for streaming on the Web today.
Describing the realtime streaming used by proprietary video streaming servers, such as those offered by Real Networks and Microsoft, Burst says audio and video data is transmitted at a constant bit-rate, recorded into a buffer on the client machine, and played at the same rate at which it was transmitted. To allow the buffer to fill without a long delay before playback starts, the buffer is kept very small. When fluctuations in the network environment prevent a constant flow of data, the buffer is quickly depleted, and the data delay or loss shows up on screen. To minimize the problem, the bit-rate has to be limited to the minimum bandwidth one can expect to achieve over the type of connection being supported.
In HTTP streaming, meanwhile, the bit-rate of the streaming isn’t limited by the bit-rate of playback; the buffer fills as quickly as the connection will allow. However, there’s no prioritization of the way in which multiple requests for streamed data are filled. An HTTP server attempts to deliver each client as much data as possible as quickly as possible until delivery is complete. That means the client with the biggest pipe can hog a big chunk of first mile bandwidth, without regard for the effect on any other clients.
According to Burst, content providers using Burstware avoid these problems by “bursting” data from their servers to their clients. A “Conductor” component monitors server activity and distributes bandwidth demand evenly, avoiding overload. The servers, meanwhile, continuously monitor the buffer levels and available bandwidth of each client. Whenever bandwidth is available, Burstware replenishes the client-side buffers with managed “bursts” of content, prioritizing those clients whose buffers are nearest to depletion. That allows the clients to play for longer out of their buffers when demand for video bandwidth is high or data flow is interrupted. It also means that the video can safely be encoded at the average bit-rate supported by the connection type, rather than just the minimum bit-rate, which in turn allows higher image quality.
The catch is that a media player must be “Burst-enabled” to work with a Burstware server. So far, Burst has made available Burst-enabled versions of Windows Media Player and the QuickTime for Windows Player. The system works with any media type supported by these players, including MPEG-1, .avi, .mov, H.263, and Sorenson Video. Developments like Burstware, Akamai, and MPEG-4 highlight one of the great strengths of the Internet as a delivery medium: the flexibility of a system that is implemented primarily in software. True, the hardware infrastructure has to be in place to make media delivery possible, but it doesn’t have to be ripped out and replaced to allow improvements that can boost the quality of the end-user’s experience. That bodes well for everyone who’s ready to invest their content creation skills in the evolving world of Net media.
Phil DeLancie is a freelance writer based in Berkeley, CA.
