Commentary: Is Smooth Streaming Microsoft's Trojan Horse?

本文首次发表于 www.streaminglearningcenter.com.

I’ve written before that most consumers couldn’t care less if Microsoft pulled the plug on Silverlight, primarily because from their view—that of the user—it does little that Flash can’t do. 我知道, 我知道, t在这里’s lot of fringe features Silverlight offers that Flash doesn’t, 但反之亦然, and in terms of the core feature set—the features used by most web sites—and from the point of view of the user, 技术是相似的.

This doesn’t mean that Silverlight doesn’t offer multiple advantages over Flash from the developer’s perspective – it clearly does. 具体地说, if you’ve got large libraries of legacy content encoded in Windows Media format, Silverlight可以播放它, 而Flash不能. 如果你已经开发了很多应用 .Net or C#, they’re easier to port to the web using Silverlight than with Flash. The developers who created these programs can also be immediately become productive with Silverlight, while they basically have to start from scratch to produce Flash programming.

So it’s relatively clear that t在这里’s a lot of pent up demand for Silverlight from the web site producer’s standpoint. What’s holding them back from deploying Silverlight for general Internet application is the relatively low installed base of Silverlight players—still only around 33%, 而且这些数字含糊不清，未经审计.

At 33%, you can deploy Silverlight for internal or captive applications, 如何控制观众, or if your content is so compelling that you can assume that interested users will download the player to view your content. 奥运会、法国网球公开赛和温布尔登网球公开赛浮现在我的脑海中. W在这里 it doesn’t make sense is in bread and butter general Internet applications, w在这里 viewers may not want to download a plug-in to view marketing or sales oriented content. So Microsoft faces the classic chicken and egg problem – web sites won’t use Silverlight until the installed base passes some unknown tipping point, but the installed base won’t grow until web sites start using Silverlight.

The feature that they’ve created to break through this logjam is Smooth Streaming, 这似乎正在起作用. Smooth Streaming is an adaptive bitrate streaming technology that delivers a stream customized to the viewer’s connection bandwidth and adjusts that stream should conditions change. 从一个链接, 例如, the viewer on the high speed corporate LAN might get a 2Mbps stream, while the home user on a slow DSL connection might get a 500Kbps. If conditions change for either viewer—say the home user’s kids start watching YouTube videos—the video drops to a lower data rate automatically. 质量可能会下降, 但潮水仍在继续, 当孩子们上床睡觉的时候, 质量会提高.

Of course, Adobe has the same feature with Dynamic Streaming. The biggest differences are that Smooth Streaming is more proven—especially the digital rights management component—and that Smooth Streaming uses the HTTP protocol rather than RTMP. 使用RTMP有两个后果. 第一个, it requires a Flash Media Server connection with each viewer, 这意味着更高的服务器相关成本.

Second is that HTTP data is more cache-friendly than RTMP, which should translate to fewer streams delivered to satisfy the same number of viewers and better quality of service. 例如, viewer 1 on a corporate LAN or watching via an ISP would get the complete video, which would be stored on the corporation’s or ISP’s cache server. Subsequent requests for the same data would be satisfied from the cache, so the producer doesn’t have to pay the CDN to send the streams again. 因为数据基本上是在本地提供的, the subsequent viewers should also have a better viewing experience.

我以前写过这方面的文章 Streaming Gets Smarter: Evaluating the Adaptive Streaming Technologies, and have never been comfortable that the theoretical benefits of HTTP over RTMP actually translate to lower costs or higher quality of service. 例如, I've asked Microsoft multiple times to supply a Smooth Streaming user that would state on the record that Smooth Streaming was more efficient from a delivery perspective, 还没收到回音.

I’ve interviewed multiple CDNs and none have said that HTTP-based technologies allow their customers to deliver an event cheaper than RTMP. 在某种程度上, perhaps that’s because virtually all of their clients have been asking to deliver streams to the ubiquitous Flash Player, and the alternatives—Silverlight—has the aforementioned penetration issues. No sense trying to sell someone beef when they’re asking for chicken. 另一方面, 如果基于HTTP的技术更高效的话, 你可以预期价格也会随之上涨, 然后用户跟随定价. 到目前为止，这种情况还没有发生.

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