2010年12月30日
By 1月时特约编辑
专题文章

Review: Microsoft Expression Encoder 4

如果你有流媒体视频的话, one priority has to be the ability to reach iDevices, preferably via HTTP 在线直播, Apple’s adaptive product offering. 在过去, 然而, 这通常需要与第三方服务提供商签约，或者购买昂贵的硬件编码器和服务器容量. 想要在内部制作和管理iDevice产品的制作人只能选择有限的低成本替代产品. 最近, 一家只能被形容为苹果-微软的奇怪同床异梦的公司提供了一种廉价的选择.

具体地说, 这项新功能包括微软新的表达式编码器4(发布日期为2010年6月)和使用IIS实时流畅流功能的互联网信息服务(IIS) 7 web服务器. 在表达式编码器4中，您生成一个平滑流MP4比特流并传输它

到IIS服务器. 然后服务器将把传输流从MP4重新包装为苹果的HTTP 在线直播使用的MPEG-2传输流，并创建所需的 .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 costs $199.95年零售, 所需的Windows Server 2008 R2 SP1 Beta版的价格信息可在www上获得.微软.com/windowsserver2008/ en/us/pricing.aspx. Pricing is based on the edition and number of client access licenses. John Deutscher wrote an excellent tutorial of the entire workflow, including Expression Encoder and IIS Media Services, 你们可以阅读 at http://learn.iis.net/page.(参见Tim Siglin的“第一眼:IIS媒体服务”,” pp. 26–32).

在这个简短的回顾中，我要做的是通过Expression Encoder工作流程和测试Expression Encoder的质量和性能，以确定您需要哪种类型的计算机才能使其为直播工作.

Expression Encoder 4: What’s New
I 综述了 Expression Encoder 3 in December 2009. 在版本4中, the interface and workflow have changed minimally; the major difference is the opening splash screen, 哪一个 points you to three different types of projects. Transcoding projects convert files to Silverlight-compatible VC-1 or H.而Silverlight项目允许你编码和创建一个Silverlight包. Live broadcasting projects obviously let you broadcast live. I spent most of my time in this project type.

简单地说，除了HTTP 在线直播特性，Expression Encoder 4还提供了一个新的H.来自MainConcept的264编解码器，微软从内部构建的H.264 codec featured in Expression Encoder 3. This changeover was a bit surprising because the Microsoft H.264 codec performed so well in my previous tests. When I asked a Microsoft representative why the company switched, 有人告诉我，MainConcept编解码器使微软能够更快地访问High Profile支持等功能, 哪一个 is in the released version, and GPU encoding acceleration, 哪一个 is coming in a future service pack release.

Also new in Expression Encoder 4 is digital rights management, support for closed-caption files, and enhanced Live Smooth Streaming broadcasts. Microsoft does offer a trial version, but it doesn’t include the H.264编解码器.

HTTP 在线直播 by Numbers
像大多数基于软件的实时编码器一样，在直播中驱动Expression Encoder 4很简单. First, choose your source, 哪一个 can be a live or disk-based file. 然后，选择模板. 我测试了两个模板:一个用于iPhone Wi-Fi的简单模板，另一个用于要求高得多的720p模板. I’ll report the results separately later in the article. 一个红色的小矩形显示了用这个模板创建的五个文件的配置.

然后，选择一个输出，可以是IIS服务器，也可以是基于磁盘的文件. 我用的是后者. 下一个, cue the starting video and click Start, 当你开始广播后，它会变成你在图中看到的停止按钮. 整体, none of the software-based live encoders are that hard to operate, 和Expression Encoder 4应该在大多数视频制作者或编码专业人员的能力范围内.

Before you start your live event, 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, 手动将Silverlight播放器的源更改为直播或点播事件的发布点. You also have to create the HTML5 page by hand or in another program. In the service pack that I mentioned before, 微软将允许Expression Encoder在Live Broadcasting Project界面中创建Silverlight和HTML5播放器, 这是一个很好的便利. 然后，你必须把这些页面上传到网络主机上，这样它们就为活动做好了准备.

To create an on-demand broadcast for either Silverlight or iDevices, you can archive the files created during a live event, host a simulated live event just to create the files, or create the files in another new tool from Microsoft, IIS转换管理器, 我没有复习.

性能:SD广播
I tested Expression Encoder 4 on a 3.33 GHz 12核(24支持HTT) HP Z800运行64位Windows Professional和24GB RAM. In my initial trial, I tested the H.264 IIS Smooth Streaming iPhone Wi-Fi preset, 哪一个 produced three streams, 所有400x300分辨率, at 300, 400, 和800 kbps. I used an interlaced SD source from a DV camera for these trials.

顺便说一句, 请注意，为HTTP 在线直播配置流的权威来源是Apple Technical note, 你们可以阅读在这里. 微软的编码参数与苹果的建议几乎没有相似之处, 任何生产者计划使用表达式编码器4创建HTTP直播流应该检查技术说明.

我使用预设是为了简单和便于复制，以便以后在不同的计算机上进行测试.

在CPU效率方面, this first test was a walk in the park for the Z800, 哪一个 produced all three streams using about 6% of available CPU.

Video quality was generally very good, 虽然在运动序列中有明显的去隔行伪影，涉及许多尖锐的边缘. 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. 我向微软的代表询问了去隔行化的质量，他告诉我这是一项新技术, 选择混合, that will be added to the aforementioned service pack. 作为一篇社论, 对于实时事件(实际上是所有流媒体项目)，您应该尽可能使用渐进式源。. But when you’re forced to use interlaced source, 请记住，这是一个基于硬件的解决方案通常优于基于软件的解决方案的领域.

性能:高清试验
接下来，我试了H.264 IIS平滑流720p模板，它产生了五个流，从720p在2.5Mbps to 276x208 at about 260Kbps. In this trial, I used a disk-based progressive HDV file as my source.

Looking at encoder efficiency, 再一次。, the Z800 proved more than up to the task, averaging a very comfortable 40%–45% CPU utilization. Working at these high data rates, 渐进源, the quality of the encoded video stream was very good.

整体, 这种微软解决方案的吸引力在于，它能够以低廉的价格适配苹果设备, 哪一个, if you already own Microsoft Server 2008, 售价199美元.95, the price of Expression Encoder 4. Other than the deinterlacing issues I discussed, video quality was quite good, and Expression Encoder 4 ran very efficiently on the HP Z800.