2010年12月30日
By 1月时特约编辑
专题文章

微软表达式编码器4

如果你有流媒体视频的话, 首先要考虑的是能够接触到设备, 最好通过HTTP直播, 苹果的适应性产品. 在过去, 然而, this often required either signing up with a third-party service provider or buying expensive hardware encoders and server capacity. 生产商s who wanted to produce and manage the iDevice offering in-house had limited low-budget alternatives to choose from. 最近, an inexpensive option became available from a company that can only be described as a strange bedfellow for Apple—Microsoft.

具体地说, the new capability involves Microsoft’s new (ship date June 2010) Expression Encoder 4 and the Internet Information Services (IIS) 7 web server using the IIS Live Smooth Streaming feature. In Expression Encoder 4, you generate a Smooth Streaming MP4 bitstream and transmit that

到IIS服务器. The server will then rewrap the transport stream from MP4 to the MPEG-2 transport stream used by Apple’s HTTP 在线直播 and create the required .m3u8 manifest file; this file tells the iDevices playing the stream w在这里 to find and retrieve the video chunks.

Expression Encoder 4售价199美元.95年零售, and pricing 信息 for the required Windows Server 2008 R2 SP1 Beta is available at www.微软.com/windowsserver2008/ en /美国/定价.aspx. 定价基于客户端访问许可的版本和数量. John Deutscher写了一个关于整个工作流程的优秀教程, 包括表达式编码器和IIS媒体服务, 你可以在http://learn上阅读.iis.net/page.aspx/ 854/live-smooth-streaming-for-iis-7---apple-http-live-streaming (see Tim Siglin’s “First Look: IIS Media Services 4,” pp. 26–32).

What I’ll do in this short review is work through the Expression Encoder workflow and test the quality and performance of Expression Encoder to determine what type of computer you’ll need to make it work for a live broadcast.

表达式编码器4:什么是新的
I 综述了表达式编码器3在2009年12月. 在版本4中, the interface and workflow have changed minimally; the major difference is the opening splash screen, 哪一点指向了三种不同类型的项目. 转码项目将文件转换为silverlight兼容的VC-1或H.264, while a Silverlight project allows you to encode and create a Silverlight package. 直播项目显然可以让你直播. 我把大部分时间都花在了这个项目上.

Briefly, in addition to the HTTP 在线直播 feature, Expression Encoder 4 also features a new H.264 codec from MainConcept, with Microsoft switching over from the internally built H.264编解码器的特点在表达式编码器3. 这种转变有点令人惊讶，因为微软H.264编解码器在我之前的测试中表现得很好. 当我问微软公司的代表为什么要换公司时, I was told that the MainConcept codec gave Microsoft faster access to features such as High Profile support, 哪个是发布版本, 和GPU编码加速, 在未来的服务包版本中会出现哪些内容.

Expression Encoder 4的另一个新功能是数字版权管理, 支持闭标题文件, 以及增强的直播流畅流广播. 微软确实提供了试用版，但不包括H.264编解码器.

HTTP直播按号码s
Like most software-based live encoders, driving Expression Encoder 4 in a live broadcast is simple. 首先，选择源文件，它可以是活动文件或基于磁盘的文件. 然后，选择模板. I tested two templates: one easy one for the iPhone Wi-Fi and one for the much more demanding 720p template. 我将在本文后面单独报告结果. A little red rectangle shows the configuration of the five files created with this template.

Then, choose an output, 哪一个 can either be the IIS server or a disk-based file. 我用的是后者. 下一个, 提示开始视频并单击“开始”, 哪一个 turns to the Stop button that you see in the figure after you start the broadcast. 整体, 没有一个基于软件的实时编码器是很难操作的, and Expression Encoder 4 should be well within the capabilities of most video producers or encoding professionals.

在你开始现场活动之前, 当然, 你必须创建你的Silverlight和/或HTML5网页来托管视频. 在当前版本中, you have to first create a Silverlight project to create the player; then, manually change the source of the Silverlight player to the publishing point of the live or on-demand event. 您还必须手工或在其他程序中创建HTML5页面. 在我之前提到的服务包中, Microsoft will enable Expression Encoder to create both the Silverlight and HTML5 players in the Live Broadcasting Project interface, 这是一个很好的便利. Then, you have to upload the pages to the web host so they’re ready for the event.

为Silverlight或iDevices创建点播广播, 您可以存档在活动期间创建的文件, 托管一个模拟的现场事件来创建文件, 或者在微软的另一个新工具中创建文件, IIS转换管理器, 我没有复习.

性能:SD广播
我在3上测试了表达式编码器4.33 GHz 12-core (24 with HTT enabled) HP Z800 running 64-bit Windows Professional with 24GB of RAM. 在最初的试验中，我测试了H.264 IIS流畅流iPhone Wi-Fi预设, 产生了三条溪流, 所有400x300分辨率, at 300, 400, 和800 kbps. 我使用了来自DV相机的隔行SD源进行这些试验.

顺便说一句, note that the definitive source for configuring streams for HTTP 在线直播 is the Apple Technical Note, 你们可以阅读在这里. The Microsoft encoding parameters bear little resemblance to Apple’s recommendations, and any producer planning to use Expression Encoder 4 to create streams for HTTP 在线直播 should check the Technical Note.

I used the canned presets for simplicity and ease of duplication should I need to test on different computers later.

在CPU效率方面, 对于Z800来说，第一次测试就像在公园里散步一样轻松, 它使用大约6%的可用CPU生成所有三个流.

视频质量总体上很好, though t在这里 were noticeable deinterlacing artifacts in motion sequences that involved lots of sharp edges. 我检查了去隔行处理选项，发现鲍勃是我唯一的选择, 不过我可以让它失效. I asked the Microsoft rep about deinterlacing quality and was told about a new technique, 选择混合, 这将添加到前面提到的服务包中. 作为一篇社论, you should use progressive source whenever possible for live events (and all streaming projects actually). 但当你被迫使用交错光源时, remember that it’s one area w在这里 hardware-based solutions are usually superior to software-based solutions.

性能:高清试验
接下来，我试了H.264 IIS Smooth Streaming 720p template, 哪一个 produced five streams, from 720p at 2.5Mbps到276x208，大约260Kbps. 在这个试验中，我使用了一个基于磁盘的渐进式HDV文件作为我的源文件.

看看编码器的效率, 再一次。, 事实证明，Z800完全可以胜任这项任务, 平均40%-45%的CPU利用率. 在如此高的数据速率下工作, 渐进源, 编码后的视频流质量非常好.

整体, the attractiveness of this Microsoft solution is the inexpensive ability to adaptively distribute to Apple iDevices, 哪一个, 如果您已经拥有Microsoft Server 2008, 售价199美元.95，表达式编码器4的价格. 除了我讨论过的去交错问题, 视频质量相当不错, 表达式编码器4在HP Z800上运行得非常高效.