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About IIS Smooth Streaming

With Microsoft Expression Encoder, you can encode videos that take advantage of Smooth Streaming technology. Smooth Streaming is the Microsoft implementation of adaptive streaming technology, which is a form of web-based audio/video content delivery that uses HTTP progressive download technology. Instead of delivering content by downloading, or in a CBR (constant bit rate) stream, the content is delivered to the client in a series of fragments. As the client plays the fragments, network conditions may change; for example, bandwidth may decrease, or CPU power may become compromised. Should any of this deterioration of playback conditions occur, the client can request fragments from the server that are encoded at lower bit rates, in order to compensate for local system conditions. Conversely, should playback conditions become better, the client can request playback fragments encoded at higher bit rates.

In effect, this enables the client to continue playing back media without stuttering, buffering, or freezing. As a result, users experience the highest-quality playback available, with no interruptions in the stream.

Using HTTP delivery stands in contrast to the previous use of streaming protocols such as Real Time Streaming Protocol (RTSP) or Real-time Transport Control Protocol (RTCP), and others, to deliver media over the web. Although streaming protocols provided many features that allowed for good media streaming, HTTP delivery is more optimized for the web because the web itself is fundamentally engineered for HTTP delivery of content. Adaptive streaming technology, represented in Smooth Streaming, is a hybrid of HTTP delivery technology and streaming protocol innovation.

As an end user, all that you need to take advantage of Smooth Streaming playback is Microsoft Silverlight. However, using Expression Encoder, you can encode Smooth Streaming video or develop Silverlight clients that use Smooth Streaming technology. If you are a content provider, you will need Microsoft Windows Server 2008, Microsoft Internet Information Services (IIS), the Smooth Streaming extension for IIS7, and Silverlight to deliver the full Smooth Streaming experience.

Although a Silverlight client is necessary if you want to take advantage of adaptive streaming, you do not have to encode using a Silverlight template. You can encode a simple WMV file as an adaptive streaming file and still benefit from the progressive download capabilities.

In Expression Encoder, you have a choice of creating two types of adaptive streaming files. You can create an IIS Smooth Streaming file or an IIS Smooth Streaming Single File. Both require that you stream them from Microsoft Windows Server 2008 with IIS 7 and the Smooth Streaming extension for IIS7. The IIS Smooth Streaming output format creates several final files, whereas the IIS Smooth Streaming Single File produces just one file.

When you encode a media asset using either the IIS Smooth Streaming or IIS Smooth Streaming Single File output format, Expression Encoder creates the following file types:

  • *.ismv    This is an MP4 file that contains both video and audio content. If you chose to encode an IIS Smooth Streaming file, Expression Encoder creates one .ismv per bit rate. For example, if you specified that you wanted your video encoded using four different bit rates, Expression Encoder creates four .ismv files. However, if you chose to encode an IIS Smooth Streaming Single File, Expression Encoder only creates one file that contains streams of each bit rate.

  • *.isma   This is an MP4 file that contains only audio content. If you had encoded an audio-only file, this is the format that results. As with .ismv files, depending on your output choice, Expression Encoder creates several .isma files or just one.

  • *.ism   This is an XML file called a "server manifest file." It describes the relationships between media tracks, bit rates, and the files on disk. Only the IIS Smooth Streaming server uses this file.

  • *.ismc   This is an XML file called a "client manifest file." It includes important information about the encoded file, such as the encoded bit rates, the codecs used, and other information. Only the Silverlight playback client uses this file.

You can publish your encoded file to an IIS server by using the WebDAV publishing plug-in available by default in the Publish category on the Output tab. For more information about publishing your video, see Publish your media. Once the video is published, IIS delivers it to the Silverlight client for viewing by the user.

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