便携式蜂窝/Wi-Fi视频广播单元回顾:宜必思DMNG

这是什么??
法国的 AVIWEST's 宜必思DMNG is a portable SDI or composite video wireless link that uses Wi-Fi or cellular technology to transmit your live or archived video back to a remote server on the internet, 然后将视频呈现为SDI或合成视频.

我什么时候用它?
If you were a sports or news journalist wanting to send high quality images back from an outside the studio to your broadcast center, or if you needed an ad-hoc video connection from a location with no fiber or telecom access and you wanted more flexibility than a satellite link (perhaps where there is no line of sight, 或者没有时间设置你的卫星链接). Incidentally this type of link is called generically -"contribution feed"-just in case you see me use this term below).

宜必思DMNG

听起来像广播套件-为什么它在流媒体?
1)它使用IP流技术来工作(稍后会详细介绍)
2)许多网络广播员和流媒体直播工程师将把这视为他们工具箱中有用的一部分

它与StreamBox, Quicklink和LiveU相比如何?
虽然每个人都有优势, 这是一种较新的设备, 并受益于“最新”的一系列这类产品. Rather than break this technology into the streaming sector with too much accolade I am arranging to conduct a proper benchmark of each of these products as a separate feature later this year. 不用说，这个产品本身就给我留下了深刻的印象.

Background
在过去十年的大部分时间里，我都在使用VSAT技术进行投稿, 特别是当我们想要从一个事件中获得2小时的实时信息时. 它依靠的是一辆车顶上有卫星连接的大型货车, 提前一个小时左右在现场准备好菜. 服务费用随你需要的带宽而变化, 但从本质上讲，它类似于便携式租用线路. 虽然它在一般情况下是有效的, there was little resilience in the system and so a there was a high risk that factors such as rain-fade, 缺乏视线, 运营商或集线器问题, 等等都可能导致导致整个事件失败的问题. 很长一段时间, 虽然, it was the only option for sending 512Kbps images live out on the internet without calling out for a full-blown TV production team.

常用的移动电话网络, 传统上只支持非常低的比特率，没有保证的QoS, 总是引起网络广播员的兴趣吗. It has seemed for a long time that the ubiquity of IP via cellular would eventually emerge to become a contribution feed technology. 就在我所在的英国, 例如, 大多数蜂窝网络运营商将E1放入蜂窝基站的底部(这是一个宽泛的规则), 当你进入大都市地区，情况会有很大的不同). E1为运营商提供了2Mbps，可以在所有可能使用该蜂窝的电话上共享. If a webcaster turns up and saturates that entire 2Mbps (and if they conjecturally could take a priority over all the other wireless 3G users in the area) then no one else would be able to use that cell for that period of time. 没有手机网络运营商会这么做.

Equally to provision every cell with an extra E1 "just in case" a webcaster wants to use it requires a whole lot more regular use and justification/demand for the service than exists.

那么，一个网络广播员如何将高比特率的贡献反馈流到他们的服务中心呢?

在过去的几年里，3G多路复用器改变了一切. 3G多路复用器通常由四个网络运营商连接服务. It "bonds" these together in the field and presents them as a single consolidated service to the device in the operator's hand. 这意味着操作者可以访问, 说, 4家运营商的4个300Kbps区段, 但加在一起似乎是1200Kbps.

Now since he is contending with many other users on the cell network it is important to 不e that this 300Kbps may vary from minute to minute. 这是不 QoS保证服务——它是一种“尽力而为”的服务. 由于这些接入电路是“网络中立的”，争论有点像面包之争, 因此，在这种情况下，基于多路复用器的系统必须能够适应动态变化. 这正是他们所做的. 随着带宽的下降, 编码质量降低:流变得更像素化和更低的分辨率, but if the technology works properly there is a continuity of audio and regular enough motion in the image that the viewer's brain can actually compensate until the quality recovers.

For this reason these technologies are suited to "extreme" cases where there are no alternative connections such as leased lines, 纤维, 以及能够提供更好的服务质量的卫星.

但随着网络摄像头的普及，观众已经习惯了低质量的视频, 手机摄像头, YouTube, 等等......, even broadcast media commonly makes extensive use of low bitrate images: The key is that if this is the only way to capture the content that 每一个人 想看的话优先考虑的是得到的内容无论质量如何.

回到宜必思DMNG v2
我设法赶上了理查德·帕蒂森和他在天空新闻技术团队的同事, 谁已经测试了包括DMNG在内的各种产品. 他们已经测试了大约一个月, al虽然 they missed the recent student riots in London which would have provided a great opportunity for them to "test it in anger" since that is exactly the scenario where this type of technology comes into its own. In that cynical way that we in the industry sometimes wait for a "good disaster" to happen I have asked Richard to let me know how it fares when they finally to get a change to use it "in anger."

首先突出的是这个装置的紧凑尺寸. 和一盒巧克力一样大小的, 它最初回避了一个问题:“剩下的钱在哪里??“这个东西是 small-重量少于2磅(1公斤), 大约一封商业信件大小的足迹, 有一英寸多一点深.

Having something this small that functionally (in many ways) replaces an entire outside broadcast truck is, 在我的小怪胎世界里, 绝对 疯狂的. 我怎么强调都不为过.

If you had told me in 1998 (when I started looking at delivering my first IP VSAT live streams) that ten years later a van, 菜, 校准工具, 视频编码器将被一个可以放在手里的单元所取代, 我一定会印象深刻的. 十几年后，我拿着那个盒子，看到它还能正常工作，真是太让人兴奋了.

IBIS摄像机

崎岖的, 现场准备单元具有SDI和复合接口，允许您直接连接相机. 又小又轻, the cameraman can either wear it on his belt or can even clip it onto their flash-shoe horn on their camera. 它可以用自己的电池以2Mbps的速度运行一个小时, 也可以使用标准相机电池, 因此，外出走动时，无需耗尽电源.

一旦配置好了(通常是在主基地)，接下来就是一个简单的“开机等待”过程. 启动需要一两分钟，然后, 很简单, at the remote end (where ever that server may be on the internet) the SDI output presents the picture the camera is producing.

Interestingly the server can receive four feeds at once and (it has a Windows 7-based PC at its heart) you can then simply click on which feed you want to output to the SDI for seamless switching. I am informed that the next version will have four SDI out cards so all four signals can be sent to production in parallel.

延迟是一个经验丰富的人会问的问题:嗯, 在DMNG上它是可切换的:我们测试了5秒设置和3秒设置. 令人惊讶的是，它确实做到了它在罐头上所说的:5秒或3秒延迟. At 3 seconds we found that the artifacting and pixilation was more common-particularly if there was a significant change in the signal strength and often resulting in a 3s freeze of video, 但音频播放还不错. )别相信我? 请查看下面的测试视频.)

一个非常好的功能是回话功能. Often talk back to the studio to cue the presenter up with the live bulletin has required 不hing more complex than a cell phone. However during a report it's hard for the reporter to look professional with a cell phone pressed to her ear. DMNG允许将生产通信环路，以便演示者可以, 通过同样的链接, 和工作室谈谈. 更棒的是，还有一个计数灯连接，所以当摄像头信号是实时的时候，它是清晰的. 不要再说“哦，妈的，这是现场直播吗???“要上电视了.

你知道吗? 从用户的角度来看，就是这样. 是的，如果您想手动调整H，则有多种配置.基于264的编解码器设置，如输出大小和格式. 您可以从设备或服务器更改和管理手机加密狗. 等等....... But this is 不 something you want to tinker with in the field unless you are stuck; it's best set up once and then just left to charge and use with a single press of the power button.

这就是我喜欢宜必思DMNG的原因. 如果你问我的话，我觉得它离内置到相机里还有一步之遥. 我可以预见下一代将利用自适应比特率, 摆脱目前使用的劣等可变比特率模型, 因为ABR需要太多的CPU来压缩到这种形式. 一旦完成, I can then see this technology being miniaturised to the point it comes as standard on the smart phone (perhaps that's why Skype just acquired Qik?).

但是现在, the DMNG is a professional solution to a problem that has troubled the professionals for year: ultra-portable, 超快的, 特别视频贡献.

Expect to see footage both on TV and online that uses this GREAT example of intelligent streaming media innovation on a screen near you very soon.