inlet technologies - powering smooth streaming

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White PaperRev A. Nov 09.

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IntroductionIn October 2008, Microsoft announced that Internet Information Services (IIS) 7.0 would feature a new HTTP-based adaptive streaming exten-sion: Smooth Streaming. To promote this new technology, Microsoft also created an initiative with Akamai and launched a showcase Web site—SmoothHD.com—that highlights the aspects of Smooth Streaming.

At the Mix09 conference of March of this year, Microsoft announced support for both Live and On Demand video in Smooth Streaming, and demonstrated Live Smooth Streaming publicly for the first time. They were able to do this through their partnership with Inlet Technologies.Before Smooth Streaming, video on the web has always been plagued by 2 major issues: the quality of the video and the reliability of the playback. Viewers are disappointed if the video quality is poor (either too small or too blurry) or frustrated if the playback is unreliable (constantly rebuffering or stuttering). It always seemed like both of these issues were persistent; rarely could the end user enjoy a high quality video that could be reliably played back at the same time. Smooth Streaming solves both of these issues by making the experience of playing video from the web exactly like watching a TV: it plays instantly and is always the highest possible quality that will reliably play back.

How it WorksSmooth Streaming dynamically detects local bandwidth and CPU conditions and seamlessly switches—in near real time—the video quality of a media file that a player receives. This ensures that consumers with high-bandwidth connections can experience high definition (HD) quality streaming while those with lower bandwidth receive the appropriate stream for their connectivity. Smooth Streaming allows consumers across the board to enjoy a compelling, uninterrupted streaming experience. It also alleviates the need for media companies to cater to the lowest common denominator of quality level within their audience base.

Content producers will be able to boost brand awareness and advertising revenues by extending average viewing times through higher quality true HD (resolution greater than 720p) experiences. They can also benefit from unprecedented network scalability using distributed HTTP-based Web servers and offer better quality to more customers.

Inlet’s full line of products now offers support for Smooth Streaming, giv-ing content creators options for both Live and Video On Demand delivery options utilizing Smooth Streaming. With SpinnakerTM and the Spinnaker Management Console, users can set up and schedule live smooth streaming events. With Fathom® and Armada, users can generate the necessary assets to support on demand options.

A New Content Delivery OptionPrior to Smooth Streaming, media delivery on the Web used two delivery methods: progressive download and traditional streaming. Popular video sharing Web sites, including YouTube, Vimeo, and MySpace almost exclusively use progressive download. This is nothing more than a simple file download from an HTTP Web server. The term “progressive” stems from the fact that most player clients allow the media file to be played back while the download is still in progress—before the entire file has been fully written to disk (typically to the Web browser cache). If you pause a progressively downloaded video at the beginning of playback and then wait, the entire video will eventually have downloaded to your browser cache, allowing you to smoothly play the whole video without any problems. HTTP is known as a stateless protocol, meaning if an HTTP client requests some data, the server responds by sending the data, but won’t remember the client or its state. Each HTTP request is handled as a completely standalone one-time session.

RTSP (Real-Time Streaming Protocol), on the other hand is an example of a traditional streaming protocol, though only one of many versions of streaming protocols for the web. RTSP is defined as a stateful protocol, which means that from the first time a client connects until the time he/she disconnects, the streaming server keeps track of the client’s actions. The client communicates its actions, or states to the server by issuing commands such as PLAY, or PAUSE. After a session between the client and the server has been established, the server begins sending the media as a steady stream of small information packets (the format of these packets is known as RTP).




Smooth StreamingSmooth Streaming is a hybrid delivery method that acts like traditional RTSP style streaming but is based on HTTP progressive download. It’s an advanced concept that uses HTTP rather than a new protocol. It relies on HTTP as the transport tool and performs the media download as a long se-ries of very small progressive downloads, rather than one big progressive download. It is one version of what is generically called adaptive stream-ing, a new and innovative way of streaming media and solving the issues of reliable playback and quality.

Adaptive streaming offers the following advantages over traditional streaming to the content distributor:• Lower costs to deploy because adaptive streaming can use generic HTTP caches/proxies and doesn’t require specialized servers at each node.• Better scalability and reach, reducing “last mile” issues because it can dynamically adapt to inferior network conditions as it gets closer to the

user’s home.• Adaptability, because it accommodates the audiences’ content, rather than requiring content providers to guess which bit rates are most likely to

be accessible to their audience.

For the user it offers the following benefits:• Fast start-up and seek times because start-up/seeking can be initiated on the lowest bit rate before moving to a higher bit rate.• No buffering, no disconnects, no playback stutter (as long as the user meets the minimum bit rate requirement).• Seamless bit rate switching based on network conditions and CPU capabilities.• Consistent and smooth playback experience.

In a typical adaptive streaming implementation, the video/audio source is cut into many short segments (“chunks”) and encoded to the desired deliv-ery format. Chunks are typically 2 to-4 seconds long. At the video codec level, this typically means that each chunk is cut along video GOP (Group of Pictures) boundaries (each chunk starts with a key frame) and has no dependencies on past or future chunks/GOPs. This allows each chunk to later be decoded independently from the other chunks, but when collected and played back by the end user it is viewed as an uninterrupted video experience.

The encoded chunks are hosted on a HTTP Web server. A client requests the chunks from the Web server in a linear fashion and downloads them using plain HTTP progressive download. As the chunks are downloaded to the client, the client plays back the sequence of chunks in linear order. Because the chunks are carefully encoded without any gaps or overlaps between them, the chunks play back as a seamless video.

The “adaptive” part of the solution comes into play when the video/audio source is encoded at multiple bit rates, generating multiple sized chunks for each 2-to-4-seconds of video. The client can now choose between these various chunks that suit its needs best. Web servers usually deliver data as fast as network bandwidth allows. The client can easily estimate user bandwidth and decide to download larger or smaller chunks ahead of time. The size of the playback/download buffer is fully customizable.

Encoding Smooth Streaming Assets with InletVideo on DemandBoth Fathom and Armada, Inlet’s Video on Demand solutions, support creating Smooth Streaming assets. For customers in need of quickly gen-erating Smooth Streaming VOD assets, Fathom allows users to create jobs and templates that identify all the necessary bit rates and resolutions desired. Armada expands on this, allowing users to manage smooth streaming encodes across a farm of dedicated encode servers, allowing for a huge increase in productivity and time to market.

A single media asset is identified and then converted into all of the resolutions and formats needed to support the desired resolutions. In addition to audio and video files, other files that describe the details of the assets (called Manifest files) are also needed to support Smooth Streaming. Both Armada and Fathom will automatically generate the necessary Manifest files directly for the client. Armada takes this a step even further, by allowing users to configure customized manifest files. This will enable content creators to make unique user experiences without re-encoding the collection of assets.

A typical Smooth Streaming media asset therefore consists of the following files:• MP4 files containing video/audio

• *.ismv - contains video and audio, or only video• 1 ISMV file per encoded video bitrate• *.isma - contains only audio

• In videos with audio, the audio track can be muxed into an ISMV file instead of a separate ISMA file• Server manifest file

• *.ism• Describes the relationships between media tracks, bitrates and files on disk• Only used by the IIS Smooth Streaming server - not by client• Client manifest file• *.ismc• Describes to the client the available streams, codecs used, bitrates encoded, video resolutions, markers, captions, etc.




Smooth Streaming Manifest FilesThe Smooth Streaming Wire/File Format specification defines the manifest XML language as well as the MP4 box structure. Because the manifests are based on XML they are highly extensible. Among the features already included in the current Smooth Streaming format specification is support for:• VC-1, WMA, H.264 and AAC codecs• Text streams• Multi-language audio tracks• Alternate video and audio tracks (i.e. multiple camera angles, director’s commentary, etc.)• Multiple hardware profiles (i.e. same bitrates targeted at different playback devices)• Script commands, markers/chapters, captions• Client manifest Gzip compression• URL masking• Live encoding and streaming

Both manifest file formats are based on XML. The server manifest file format is based specifically on the SMIL 2.0 XML format specification.

A folder containing a single Smooth Streaming media asset might look something like this:

Live Encoding SolutionInlet’s Live Encoding solution, Spinnaker, supports live Smooth Streaming – a first in the industry. Spinnaker allows customers to control all the setting necessary to encode and publish Smooth streams to an IIS server. Spinnaker Management Console, Inlet’s dashboard for managing multiple encoders. This further allows customers with large scale broadcasting needs to control multiple encoders simultaneously; enhancing the Smooth streaming experience by allowing customers to use multiple spinnakers for one event to provide a wider range of resolution options, guaranteeing their viewers the best possible consistent playback and highest quality.

Just as Fathom and Armada do for VOD, Spinnaker creates Manifest Files and send them to the IIS server along with the video streams, letting the server and eventually the client player (e.g., Silverlight) know which resolutions are avail-able for playback.

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Building Out a Smooth Streaming ArchitectureFor VoDContent creators with small amounts of video to encode as Smooth Streaming VOD assets can use Fathom. Those needing to capture from tape as part of their workflow can take advantage of the Fathom HD Turnkey Workstation. Customers with larger amounts of content or needing the ad-ditional benefits of Inlet’s Pre-Encoding Analysis and Post Encode Features to help sort, manage, and QC their content can use Armada.

For LiveLive Event producers wishing to encode Standard Definition Smooth Streaming can use one or more Spinnaker 5000. Those wishing to encode High Definition Smooth Streaming events will use one or more Spinnaker 7000, and producers who want more than four resolutions available per event will need the Spinnaker Management Console allowing them to manage and synchronize multiple Spinnakers for events in one easy to use interface.

Both Live and VOD customers wishing to use Smooth Streaming will also need an IIS server supporting Smooth Streaming (IIS 7) and a Silverlight player. Akamai is the first CDN to offer Smooth Streaming support for customers, though more will be added in the second half of 2009.

SummaryThanks to Smooth Streaming, the experience of watching video online is now as reliable and high quality as what users associate with their TV today. Playback starts nearly instantly, never pauses or has to buffer, and plays back the highest possible quality video without the users having to guess their connection speed.

Whether you need to deliver live or on-demand content, Inlet’s advanced encoding solutions produce the highest quality video, faster and more ef-ficiently than any other solution. To learn more, visit www.inlethd.com, or call 1-866-96-INLET.

inlet technologies - powering smooth streaming

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