2012年3月29日
By 1月时特约编辑
专题文章

买方指南:便携式捕获和转码

本文刊登在…的二/三月号 流媒体 杂志，年度 流媒体行业资料手册. 在这些买方指南文章中, 我们并不声称涵盖某一特定类别的所有产品或供应商, but rather provide our readers with the 信息 they need to make smart purchasing decisions, sometimes using specific vendors or products as exemplars of those features and 服务s.

Anytime you shoot an event accessible to power and connectivity you should consider streaming it live, 哪一种既简单又便宜. 要做到这一点, 虽然, you'll need a 软件程序 or device to encode the signal and send it to a streaming server. You have two basic choices; dedicated appliances, and 软件程序s.

我们将在本文中研究这两个类别, 但是要做好准备, 让我们来讨论影响你选择标准的两个趋势. 短暂的, 在过去, 直播时, your on-site encoder created all streams and transmitted them to a streaming server for distribution. (A features table comparing leading portable hardware encoders is at the end of this page; a similar table for software encoders is at the end of 第二页.)

例如, If you were streaming live to Flash desktops and HTTP 在线直播-compatible (HLS) mobile devices, 你需要两套编码器, or one high-performance encoder capable of producing streams for both formats. 如果你是自适应流媒体, 您需要能够产生多个流的编码器, plus the outbound bandwidth required to deliver those streams to the streaming server. These requirements often necessitated multiple encoding systems and strained the outbound bandwidth capabilities many event locations.

Today, two commonly available features of streaming servers reduce these requirements. 首先是 transmuxing, or the ability to convert the container format and/or distribution protocol of an incoming stream and repurpose it for multiple outputs. 例如, most streaming servers today can input a set of adaptive streams encoded for Flash distribution and repurpose it for HLS devices. 除了, Microsoft's Information Internet Server (IIS) can repurpose a Silverlight Stream for HLS output.

第二个特点是 实时转码，将单个输入流转换为多个自适应流. 两个例子是 Wowza 代码转换器插件和 Haivision HyperStream 生活云代码转换服务. This capability dramatically reduces the outbound bandwidth requirements at the event, 哪个通常是最重要的生产瓶颈, 以及现场编码要求.

底线是，在选择编码器之前, you should underst和 streams required by your streaming server or streaming 服务 provider. Though we list the output formats supported by all encoders in the respective features tables, 以及设备或程序是否可以输出多个流, these features may or may not be relevant depending upon which server or 服务 provider that you use.

硬件和. 软件

你的第一个决定是硬件设备vs. 软件程序. The biggest difference is cost; portable transcoding appliances can cost $10,000或更多, while the Adobe Flash Media 生活编码器是免费的，其他的要199美元以上.

The advantages of the appliances are ease of use, audio/video connectivity, and stability. 关于易用性, you can pre-configure your appliance in the office and hand it off to non-technical users for carrying to the event. So long as they can turn the appliance on and connect the audio/video feeds, 他们应该可以走了. If something goes wrong, you can log in and troubleshoot the device from your office. While software encoders aren't rocket science, none are quite this simple.

In terms of connectivity, the only format most notebooks can handle without an adapter is FireWire. 如果您没有运行DV或HDV设备, 您需要一个用于模拟或SDI输入的外部适配器, 哪个可以花费1美元,000或更多.

关于稳定, 尽管所有的设备本质上都是装在盒子里的Windows电脑, they tend to be more stable than notebooks because they're single-purpose devices. 用户不加载微软办公软件, Adobe Creative Suite, 和/或其他应用程序, 更不用说最新的共享软件或免费软件应用程序和浏览器插件了, 这能促进稳定性和一致的性能.

说到性能, don't expect a hardware appliance to have magical powers to output many more streams than a similarly configured notebook. 它们只是电脑, 毕竟, 和ir performance will be similar to a notebook of similar configuration.

在硬币的另一面, 除了价格, the biggest advantage of software encoders is the availability of production-oriented features on some programs, 比如多摄像头切换, 标题和过渡.

选择硬件设备

第一个功能表显示了来自不同供应商的三个设备. These are the most expensive web-oriented models available; if you don't need HD output or high-end connectivity, 你几乎肯定能找到更便宜的型号.

螺母和螺栓

在购买任何系统之前, make sure that it connects to your audio/video gear and meets your basic output requirements. 所以你应该:

Find the model that connects to your current audio/video gear and any planned purchases. This means details like A/V connections and whether your audio inputs are line or microphone powered.
Find the model that provides the required output format or formats in the required resolution and stream count. 正如前面提到的, start by identifying the requirements of your streaming server or servers, 或者你是否会使用流媒体服务器, 因为一些硬件编码器包括服务器组件. If you'll be serving different target devices with different formats and protocols, 评估产品时要非常具体, 因为这里的能力差别很大.

其他需要考虑的因素包括:

车载显示器. 大多数设备包括USB端口和VGA接口, 所以你插入一个键盘, 鼠标和显示器，可直接驱动各单元, 或者通过另一台计算机登录每个单元. 然而, 思科和ViewCast通过LCD和其他仪表提供反馈, the Digital Rapids TouchStream includes an 800x480 touchscreen for operation and video preview.
视频和音频调整. 有些系统启用亮度, 对比, 色调和饱和度调整以及音量控制, which are useful if you can't adjust the camera or audio recording system directly. Some also enable noise gate capabilities with varying levels of automatic gain control.
调度和GPI触发器. 如果需要远程控制开始和停止编码，则非常有用.
连接到中央控制. Useful if you need to coordinate several encoders from a single location via a centralized control system.

其他因素

除了这些客观特征——表格项目, 硬件设备在易用性和输出质量方面各不相同. 如果你无法在公司内部找到测试设备, 您可以通过产品评论或社区论坛上的评论来评估这些. Digital Rapids includes links to TouchStream reviews by myself and Tim Siglin on their TouchStream产品页面.

Though not directly on point, the ViewCast 4100 uses the same interface as other ViewCast encoders. 你可以阅读我对Niagara 2120 生活 Encoder的评论 http://bit.ly/u17JPd 观看我在尼亚加拉2100上制作的视频 http://bit.ly/uDDQiE.

便携式硬件编码器