IP video distribution
Dec 1, 2009 12:00 PM, By Mark Hershey
In practice, you will likely limit the Internet media output strategy to only one of several competing formats. The choice is often driven by the preferred development environment for your existing Web presence. If you already develop in Adobe Flash or use Adobe's Flex environment, Flash Live is a logical choice. If you develop in Silverlight, the Microsoft Smooth Streaming option is appropriate.
Both are examples of adaptive streaming, which offers a quality playback experience (including up to full 1080p HD) by creating multiple streams at different data rates simultaneously from the source content and delivering the one most appropriate for each individual viewer. That's good news to viewers because they experience minimal buffering time, fast startup time and an optimized viewing quality. But these new technologies multiply impact on your IP network and for most practical applications force a non-Internet uplink connection to a CDN. A typical adaptive streaming scenario includes as many as 11 simultaneous streams, although most installations use about five or less in actual practice.
Just how much bandwidth will live adaptive streaming demand of the network? Using Alex Zambelli's Microsoft Smooth Streaming bit rate calculator at alexzambelli.com/WMV/MBRCalc.html, to deliver five streams configured to reach a good cross section of users at a maximum of 1280 × 720 pixel playback frame size, create five streams of 400kb/s, 662kb/s, 1095kb/s, 1813kb/s and 3000kb/s. Frame size ranges down to 320 x 176 for some smaller devices. Bit rate supports 3Mb/s for well-connected users down to 400kb/s for mobile devices capable of receiving the same stream format.
But, most mobile devices in use today are not equipped to play the same stream formats used for normal Internet streaming for PCs, set-top boxes, game consoles and the new generation of network-enabled TVs. This is becoming less true as more mobile devices support Flash and Silverlight using H.264 compression, but for now there are several different compression technologies and distribution methods in common use.
iPhones are special cases. The encoder must create one or more H.264 streams (three are recommended), delivered as MPEG transport streams to a segmenter that in turn delivers chunked, time-sliced content to iPhone users. The segmenter may be included on the encoder or a separate service running on an in-house server, or on a server or server farm at your CDN.
At the moment, most video-enabled handheld mobile devices are limited by their network speed. A maximum rate of about 350kb/s-400kb/s is typical, configured with low bit rate mono audio in order to maximize the bandwidth available for video.
To have a broad reach to many viewers, create a large number of streams in real time, delivered via an unchallenged, well-managed, likely non-Internet-based network to a server farm (yours or those at a CDN), which in turn delivers an optimum experience to each viewer. If it seems a bit daunting to create and manage on your own encoder farm, there is another alternative: Backhaul a single full-bandwidth MPEG-2 feed to a company that specializes in transcoding and streaming in all desired formats. Yahoo! Broadcast, Level3 Communications and Real Networks are three examples of CDNs that offer such services to large network broadcasters.
Effect of on-demand video
On-demand video creates its own additional challenges for managing actual clips and segments and making them available to large audiences. Effective file-based delivery dictates that a similar number of different formats must be created and saved as files. The delivery impact on network bandwidth is similar at playback to the impact of live streaming, except that the number of simultaneous viewers is likely to be less.
Creating the different file formats is sometimes done by the live encoder as a byproduct of the live event. Many high-end encoders can be configured to save the live stream in the same media format for later playback. Other scenarios allow for the original source asset to be saved in uncompressed or lightly-compressed format and transcoded on the fly at playback as demand requires.
A future-proof comprehensive solution
The impact on the network to deliver on-demand video vs. a live stream is about the same, but hosting and managing a video library creates additional challenges to the IP infrastructure, particularly if you intend to offer long-term playback access to your ever-growing library of video clips. As the library grows, so does the number of simultaneous viewers.
Over time, you may find out that playback from the library exceeds the bandwidth consumed by the live stream operations. This is even truer if you create multiple different file formats for each video clip in order to handle several different playback experiences for different audiences. Furthermore, if you anticipate a need to repurpose the video assets, save the clip in an editable format such as MPEG-2. This creates a need for an even larger media storage array and a corresponding demand on the IP transport facilities.
One solution that can easily grow incrementally with your needs without periodic large investments is to outsource the entire video delivery operation, retaining the video capture and video asset management functions in-house. A comprehensive digital asset management (DAM) system can remotely manage the asset library as well as give you complete control over sourcing editing and access to content. Some DAM systems offer comprehensive features that help make live events available as quickly as possible after the event to on-demand viewers and completely automate ingest and delivery functions.
Whatever the size of your operation or the rate of transition to a new digital audience, there are many ways to select and configure a solution that will serve your needs well into the future.
Mark Hershey is vice president engineering for ViewCast.
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