Smooth Streaming FAQ
Q: What is Smooth Streaming?
A: Smooth Streaming is Microsoft’s implementation of HTTP-based adaptive streaming.
Q: What is adaptive streaming?
A: It is a hybrid content delivery method which acts like traditional streaming but is in fact based on HTTP progressive download. In a nutshell, it involves the content being delivered from the server to the client as a series of short HTTP downloads, rather than one long download or a constant-bitrate stream. Because the content is typically encoded at multiple bitrates and delivered as a series of small “chunks”, the client can also dynamically switch between chunks of different sizes (quality levels) depending on network bandwidth and CPU capability, allowing users to always receive the best level of video quality they possibly can.
Q: How is Microsoft enabling this new technology? Do I need to install a new plug-in or something?
A: This depends on what you’re trying to do with Smooth Streaming:
- If you are an end user – you don’t need to do anything except have Silverlight 2 or better installed on your machine. As of Moonlight 2.0 beta, Smooth Streaming is also supported on the Linux platform.
- If you are a content creator, you will need to upgrade your encoding software to one that supports encoding to the new Smooth Streaming file format (based on MP4). This currently includes the entry-level Expression Encoder 3, as well as enterprise-level encoding products from Inlet, Envivio, Digital Rapids and Rhozet.
- If you are a hosting provider or CDN, you will need to install the Smooth Streaming extension for IIS7 on your Windows Server 2008 origin servers. This component allows IIS7 to serve Smooth Streaming media assets to clients. Note that you will only need to install this on your origin servers – your edge cache/proxy infrastructure can remain unchanged, though you may need to configure to correctly pass through Smooth Streaming RESTful URLs.
- If you are a Silverlight application developer, you will need to add Smooth Streaming playback support to your Silverlight application. This can be done by either using Silverlight player templates included with Expression Encoder 3, using the Smooth Streaming Media Element provided with IIS Media Services 3.0 (final version only), or adopting the Open Video Player for Silverlight.
Q: Where can I see Smooth Streaming in action?
A: Visit SmoothHD.com for a demo of on-demand Smooth Streaming, with video content ranging up to 720p HD for those on fast connections (3 Mbps or more). Also check out the IIS.net demo which lets you simulate variable network bandwidth during playback. The only requirement to view Smooth Streaming video is a Silverlight 2 (or better) browser plugin. For a demo of live Smooth Streaming, check out Home Shopping Network’s 24-hr live shopping channel, also offering up to 720p in full-screen mode.
Q: When will Smooth Streaming be available?
A: A beta release of Smooth Streaming extension for IIS7 is already available for download. IIS Media Services 3.0 beta includes support for both on-demand and live Smooth Streaming. A final version of this IIS7 extension will be available in October 2009.
Q: I heard Live Smooth Streaming and Silverlight 3 were announced at MIX 2009. Does that mean Live Smooth Streaming is an exclusive feature of Silverlight 3?
A: No, Smooth Streaming (both live and on-demand) already works with Silverlight 2 today. The only Smooth Streaming content requiring Silverlight 3 will be content encoded with H.264 video and AAC audio codecs, since those codecs are new to Silverlight 3.
Q: How can you do live streaming from a Web server? I thought live streaming could only work with streaming protocols such as RTSP?
A: No, live streaming using plain HTTP is absolutely possible. In fact, from an architectural standpoint, live and on-demand Smooth Streaming are surprisingly similar. Encoders upload video/audio fragments to the IIS7 ingest server in real-time as a long HTTP post. The IIS7 server, upon receiving all the expected fragments for a given timestamp, appends those fragments to the Fragmented MP4 (*.ismv) files on disk and updates the manifest with the most recent timestamps. The client downloads the most recent manifest from the server when seeking or connecting for the first time, and maintains an internal incremental manifest the rest of the time.
Q: Is Smooth Streaming backwards compatible with Windows Media Services or Windows Media Player?
A: No, not at this time. Smooth Streaming serving requires Windows Server 2008 and IIS7, whereas Smooth Streaming playback is currently only supported in Silverlight applications. We hope to extend Smooth Streaming client support to other players and devices in the future.
Q: How is this streaming technology different from Windows Media MBR (multiple bit rate) streaming?
A: Windows Media Services uses traditional streaming protocols like RTSP and WMS HTTP to deliver content to clients. Content streamed with such protocols is always streamed at the rate at which it’s encoded at, which also makes it very difficult for the clients to detect overall network bandwidth and adapt to changing network conditions in a timely fashion. This means that deteriorating network conditions can’t be detected until it’s too late and the bit rate cannot be safely upgraded if the network conditions improve.
Smooth Streaming, on the other hand, is based entirely on HTTP download. This allows the clients to constantly evaluate download speeds and adapt the downloaded bit rate to the changing network conditions. Furthermore, because the Internet was predominantly built for HTTP communication, Smooth Streaming doesn’t require specialized caches and proxies and can take advantage of existing Web caches/proxies, such as the ones already built out by CDNs and ISPs. This improves scalability, accessability (no firewall issues) and reach.
Q: Does Smooth Streaming support H.264/AAC?
A: Yes. However, delivery of H.264/AAC-encoded Smooth Streaming content to Silverlight clients requires Silverlight 3, since H.264/AAC support is a new playback feature of Silverlight 3.
Q: Does Smooth Streaming support DRM content protection?
A: Yes. PlayReady Server and PC SDKs are available to all encoder ISVs and DRM ASPs wishing to implement DRM protection for Smooth Streaming. For end users, DRM services provider BuyDRM offers both on-the-fly live PlayReady DRM encryption (using Inlet Spinnaker encoders) of Smooth Streaming streams as well as offline encryption of on-demand Smooth Streaming content via their KeyOS service.
Q: Does Smooth Streaming really split up video files into thousands of chunks?
A: No, not on disk. Encoders that support the Smooth Streaming file format produce contiguous MP4 files (1 file per encoded bitrate) with file extensions *.ismv or *.isma, and manifest XML files with file extensions *.ism and *.ismc. The minimum number of files in a Smooth Streaming asset is therefore 3 files. Typically encoded assets usually include 6-8 files.
When Smooth Streaming clients request time-based slices from the IIS7 server, the contiguous MP4 files are virtually split up into fragments (chunks) by the server and sent over the wire as individual files. This allows the client requests to be cached, enabling greater scalability and efficiency.
Q: Will Smooth Streaming ensure I can deliver HD video to all my customers?
A: No. Smooth Streaming can’t perform any miracles; it’s simply an enhanced HTTP delivery method. Delivery of HD video is still bound by the efficiency of the codecs used: VC-1, H.264, etc. For example, most video experts would agree that 720p/24 video can’t be delivered at a satisfactory quality level with less than 2 Mbps encoded bitrate. Well, 2 Mbps of encoded video still requires 2 Mbps of network bandwidth in order to be delivered in real-time – and there’s nothing IIS7 or Silverlight can do to change that. After all, if there existed a way of delivering 2 Mbps of data in real-time at only 1 Mbps – wouldn’t we all be using that technology? 
What Smooth Streaming does allow, however, is for content providers to provide HD video to those customers who are able to receive it (sufficient network bandwidth and CPU power) without sacrificing the overall quality of the video or catering to the lowest common quality denominator. In other words, with Smooth Streaming content providers no longer have to guess the capabilities of their audience – instead they can simply encode to a wide range of bit rates and let the customers automatically adjust to the ones that suit them best.
Q: Didn’t Microsoft already implement adaptive streaming technology once before?
A: Yes, Microsoft developed a prototype implementation of adaptive streaming for the NBC Olympics 2008 video site. Smooth Streaming represents Microsoft’s productization of that work.
Q: What about Move Networks? Is Smooth Streaming a replacement for the Move Networks adaptive streaming plug-in?
A: No. Microsoft, as a platform company, is enabling adaptive streaming delivery for the Silverlight platform which our partners can choose to integrate into their Silverlight experiences. What Move Networks announced in 2008 was that they would be using the Silverlight client as their player component; however, they use their own proprietary technology for video delivery and do not use Smooth Streaming.
To quote John Bocharov: “From my perspective, what we offer with Smooth Streaming is a platform technology while Move Networks is a one-stop-shop service solution provider that innovates on the Silverlight platform. So I would not view this as a competing offering – the intent is to create a vibrant ecosystem of great services for streaming media to Silverlight, in which Move Networks continues and will continue to be a strong and well-respected player.”
Q: Will I need to re-encode all my content for Smooth Streaming?
A: Unfortunately, yes. Even though Smooth Streaming uses standard codecs, it requires exact temporal alignment between streams of different bit rates, as well as other encoding constraints such as closed GOPs, entry point headers, etc. We therefore recommend that you re-encode your content for Smooth Streaming from the original sources.
Q: Is Smooth Streaming based on Microsoft’s ASF file format? Or does it use some new proprietary file format?
A: No, the Smooth Streaming File Format is based on the ISO-standardized Base Media File Format, better known as the MP4 file format. It follows the ISO/IEC 14496-12 specification.
Q: Is Smooth Streaming based on new codecs? Is it restricted only to VC-1?
A: No. Smooth Streaming supports industry-standard VC-1 and H.264 (MPEG-4 AVC) video codecs, as well as WMA and AAC audio codecs. Note that delivery of H.264/AAC-encoded Smooth Streaming content to Silverlight clients requires Silverlight 3, since H.264/AAC support is a new playback feature of Silverlight 3.
Q: Why can’t I play Smooth Streaming files in my MP4 player even though you claim it’s based on the MP4 file format?
A: The Smooth Streaming file and wire formats heavily utilize Movie Fragments, a particular MP4 box structure that was originally designed with live encoding in mind. The ISO Base Media File Format specification (better known as the MP4 file format specification) covers a lot of format options and allows for a large degree of implementation flexibility. Consequently, not all developers and manufactures implement the full MP4 specification, so it’s possible that your particular MP4 reader doesn’t support MP4 Movie Fragments (“moof” and “mdat” boxes) and Smooth Streaming’s specific MP4 box structure.
Furthermore, even though SMPTE VC-1 has been officially approved for storage in MP4 containers by the MP4 Registration Authority, the MP4 file format is largely associated with H.264 video and AAC audio codecs and therefore many MP4 players only accept those codecs as valid. Finally, WMA Standard and Professional audio codecs have not been officially approved for storage in MP4 files by any standards organization at this moment so it’s possible that they may be unsupported by your particular platform.