2011年2月18日
By 1月时特约编辑
专题文章

从笔记本上进行直播

笔记本电脑上的实时事件流媒体可能是最好的, 有几个程序可以免费或相对便宜, 而且一般来说很容易使用. 但是，你需要多强大的笔记本电脑才能有效地流式传输, and how do the various live streaming software programs compare in terms of CPU requirements, 数据速率精度, 数据速率一致性和视频质量? 最后, how does the video quality of these programs match that produced by hardware appliances like the Digital Rapids TouchStream or ViewCast's GoStream SURF? 在本文中，我将尝试回答所有这些问题.

具体来说，我测试了三款笔记本电脑:一台是2.2 .基于core2duo的惠普(Hewlett - Packard).06 Ghz core2duo处理器的MacBook Pro和一个2.4核(8带HTT) i7的惠普8740w. I also tested four software programs: the Adobe Flash Media Live Encoder (free), Kulabyte XStream 2(大约10美元),000), 微软表达式编码器4(199美元).95美元)和Telestream Wirecast(495美元). 我意识到我还可以测试其他程序, but these seem to have the most mindshare in the live streaming market space. If you disagree, let me know, as this won't be the last article we write on this subject.

我是如何测试的
I tested both SD and HD inputs, testing SD on all three computers and HD only on the HP 8740w. 对SD, 我使用标准的5:50分钟4:3 SD测试文件进行测试, 我输出到DV磁带, and fed back into the various computers from my Canon XH A1 camcorder via FireWire.

我测试了5种SD场景. 首先，我在640x480@700Kbps, 480x360@400Kbps上进行了独立编码. and 320x240@200Kbps, all at native frame rate, and all at 32Kbps mono audio. Then I simulated production for adaptive streaming by producing the two lowest resolution streams (480x360 & 320x240) simultaneously, and if it looked like it was possible, all three streams. Note that for these tests, I captured all files to disk, rather than streaming them to a server.

我尽量使用每个程序的默认设置, since these should represent the software developer's view of optimum settings. 有趣的是，对于H.264编码, 我只测试了这个, Adobe默认使用基线配置文件, 微软高调出击, 并通过电视传输到主配置文件. 稍后会详细介绍.

HD测试, 我使用了几个高清源磁带, 包括对前国会议员里克·鲍彻的采访, 还有一些弗吉尼亚蓝草乐队“无速度限制”的排练录像. For HD, I tested two scenarios; first, a four stream test (1280x720@2Mbps, 848x480@1.5 mbps, 640年x360@800kbps, 和480年x270@500kbps, 所有在64Kbps音频和本机帧率)和一个单一的流848x480@1.5 mbps测试，同样是64Kbps音频和原生帧速率. 用于所有程序的所有高清测试, I captured using a BlackMagic Decklink card connected to the 8740w's Express Card slot, 捕获组件视频和模拟音频输入.

I'll present the results as follows: 第一个 I'll look at the CPU efficiency of the various programs using both SD and HD scenarios, which will tell you which programs can actually produce the necessary streams on each platform. 然后再看数据速率的准确性, 数据速率一致性, 和视频文件的质量产生的程序.

CPU效率
使用SD测试CPU利用率, 我在Performance Monitor上排队, dialed in properties that extended the measurement time to about 20 minutes and captured three minutes of video in all tested scenarios. 这产生了一个图表，如图图1 对于每个程序. 很明显, these results will tell you if you can produce the desired stream configuration(s) on your notebook using the desired program.

Ozer Notebook图1

图1. This chart from Performance Monitor shows the CPU Utilization of Telestream Wirecast in all five tests.

8710w
在惠普8710w上, 我测试了Adobe FMLE, 表达式编码器4和电视流广播, leaving out Kulabyte because the company targets HD web events that require more powerful computers. 表1 显示从各个CPU利用率图获得的结果, 说明每个任务所需CPU的百分比.

关于结果的一些说明. 第一个, the pass/fail designation indicates the presence of significant dropped frames in the captured file. 用FMLE和EE4, 这很简单, since both programs provide drop frame counters that instantly let you know when you start dropping frames.

In contrast, Wirecast displays the effective capture rate, which varies by the second. 检查Wirecast捕获的文件的适用性, 我在MediaInfo中检查了捕获后的帧率, 所有档案至少有26个.每秒98帧或更高. 我在下面提供更多关于Wirecast捕获的有效帧率的信息.

	640x480	480x360	320x240	480&320	所有
Adobe FMLE	100% -失败	65-75% -通过	45-60% -通过	100% -失败	二硝基酚
微软EE4	100% -不及格/ 85-95% -通过	75-98%及格/ 85-90%及格	50-60%通过/70-80%通过	100% -失败	二硝基酚
Telestream Wirecast	55-75% -通过	40-55% -通过	30-40% -通过	40-75% -通过	90-95% -通过

表1. 各自程序的CPU利用率.

第二个, 我用Expression Encoder 4测试了两次, 使用和不使用GPU编码, 因为它在质量和性能上产生了实质性的差异. Performance you can see in the table; in terms of quality, check out 图2. 虽然在慢动作镜头中，质量差异很小, 当行动加速时, 基于gpu的编码退化很快. 除非你是在制造纯粹会说话的人, count on using CPU-only based encoding until Microsoft resolves the issue with a release from Main Concept scheduled sometime in 2011.

Ozer Notebook图2

图2. 在运动适中的情况下，基于gpu的编码在EE4中退化很快.

顺便说一句，我使用基线配置文件而不是高测试EE4. 尽管CPU利用率保持在100%左右, EE4能够相当成功地捕获640x480流, 将5882帧中的388帧降低到25帧/秒以上. 如果你用的是速度稍快的笔记本电脑, 你可以试一试, but running at or close to 100% CPU utilization seems like a bad idea for a live broadcast.

I also tested the Adobe Flash Live Media Encoder in Main mode; which bumped CPU utilisation a hair, 但在质量上几乎没有什么不同. 郑重声明, 我在启用gpu加速的情况下测试了Wirecast, but that made very little difference in either quality or CPU requirements.

来解释结果, if you're looking for full quality 640x480 output on a Core2Duo based notebook, 无线广播是你最好的选择, though Expression Encoder 4 can get the job done in a talking head scenario where you can run with GPU-coprocessing, 或者使用基线配置文件中更快的笔记本捕获. 所有程序都可以在480x360分辨率下制作, but Wirecast is your only option for producing multiple files for adaptive bitrate streaming.

MacBook Pro
Here we get to the bait and switch portion of the review; well, kinda anyway. What I mean is that I could only get one program running on the MacBook Pro, and that was Wirecast. 我有一个版本3.1 of the Adobe FLME loaded on the notebook, but uninstalled it to load version 3.2、其中拒绝安装. 我试着回到版本3.1，但这也安装不了. 我得到了Adobe的帮助，但仍然无法让它运行起来. 我知道没有测试FMLE会让许多Mac生产商失望, 这是理所当然的, 但希望我能在随后的审查中纠正这种情况.

Ozer Notebook图3

图3. 无线广播MacBook Pro的CPU利用率.

不管怎么说, 图3 显示MacBook Pro的CPU历史记录窗口，用于我的Wirecast测试. 如你所见, Mac上的电视流非常好用, 似乎比HP 8710w的效率略高, 这也说得通，因为Mac有3分.06 GHz的CPU与惠普的2.2 GHz处理器.

MacBook Pro和Wirecast在一起的表现非常好, with all files produced in the single file tests rendered at 29 frames per second or higher. 后两个测试中产生的所有文件的帧率都是28.2 FPS或更高. Only the most discerning of eyes could tell that any frames were dropped at all.

8740w
On the 8740w I added Kulabyte XStream 2, capturing via a BlackMagic Decklink card. On this computer, I tested Expression Encoder 4 exclusively with GPU disabled. 我在表2.

	640x480	480x360	320x240	480&320	所有
Adobe FMLE	18-22%	15-18%	15-18%	20-25%	40-60%
Kulabyte XStream 2	12-15%	10-12%	7-10%	15-20%	18-25%
微软EE4	22-32%	18-22%	15-18%	15-25%	35-55%
Telestream Wirecast	12-18%	10-18%	10-12%	15-18%	18-25%

表2. 各自程序的CPU利用率.

如你所见, 在这个问题上投入CPU的力量肯定有助于解决这个问题, 作为CPU利用率百分比, the i7-based HP definitely makes all streams and combination of streams accessible from all programs. No pass/fail here - all programs produced streams without dropping noticeable amounts of frames.

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