视频捕捉加密狗买家指南

用相机捕捉到的任何事件都可以很容易地进行直播. 有无数的技术选择可以做到这一点, from encoders attached to (or even inside) the camera to dedicated standalone appliances. One of the most popular production setups is a notebook running a video mixer like 奥林匹克广播服务公司, vMix, or Wirecast 通过捕捉加密狗连接到摄像头, 哪一种既便宜又能获得所有权, 转换, 还有增加专业感的特效. 

You’ve got the notebook and software; now you need the dongle, 价格从40美元左右到700多美元不等. 这份买家指南将帮助你做出购买决定. 请注意，列出的产品具有代表性, not exhaustive; if your company has a product that should be considered with those listed please add it as a comment to the online version of this article. 

输入/输出

The first obvious concern is whether the unit connects to your camera/output device and notebook. 看看源端, 当然, 你需要输入匹配你的相机, 这通常意味着SDI或HDMI. 如果你想从其他设备广播, 像电脑一样, 你需要一个支持VGA或DVI输入的加密狗, though you’re better off acquiring the signal via the Network Device Interface (NDI) or similar protocol that vMix and Wirecast both support. 

电脑端有两个主要接口，USB和Thunderbolt. So let’s start with a quick review of USB and Thunderbolt connections and connectors. 为视角, understand that most current capture dongles attempt to transfer uncompressed video into the computer. 在1080p 30fps下，比特率约为1.5Gbps，如果你是一名游戏玩家，你想获得的60p是这个速度的两倍. 4K视频是两者的4倍，所以4K30p为6Gbps, 4K60p为12Gbps. 

与USB, remember that the standard was created to connect to and supply power to peripherals like keyboards, 老鼠, 打印机, 扫描仪, 诸如此类. In 图1 (来自维基百科)你可以看到USB 1的速度和连接器.0到USB4. 最高速度为480Mbps, USB 2.0显然不能传输未压缩的视频，这就是为什么所有USB 2.0捕获加密狗使用H.将视频传输到笔记本电脑. 即使是5Gbps, USB 3.0 can transport only a single uncompressed 1080p60 stream though it might be able to handle two uncompressed 1080p 30 streams. 

When considering both USB and Thunderbolt understand that the connector is different from the standard and related performance. So, if you see the C型连接器 on the bottom of the Figure, you could be connecting to USB 2.0, 3.0, 3.1, 3.2，或者USB 4，不过是USB 2.0是不可能的. 你怎么知道你的电脑支持哪种USB标准? 检查Windows上的“设备管理器”或Mac上的“系统信息”. 

图1. USB连接速度和连接器. 

也, remember that connecting to a faster port doesn’t increase the speed of a USB device. 不过你可以用USB 2连接.0捕获设备到USB 3.0接口时，传输速度仍然是usb2.0. 也, while it’s possible to connect multiple dongles to different USB ports on a notebook, 如果设备在同一USB总线上, 你还是可以挤上公共汽车的. So, check and make sure that your notebook has two USB busses that you can access before buying multiple dongles. 

要明白，即使你的笔记本有两个独立的USB 3.0总线可能没有足够的RAM或CPU来混合传入的馈送. In these cases, consider connecting your cameras to an inexpensive switcher like the Revesun HDMI 2x1 Multi-Viewer with PIP 并将输出信号输入到捕获加密狗中. 你可以在切换器上切换摄像头, 保留总线带宽和CPU周期，仍然添加标题, 石板, 和其他内容到选定的饲料通过您的混合软件. 

USB被设计用来连接外设的地方, 迅雷的设计, 在某种程度上, to displace the Mac Mini显示 port with a device that could function as both a 显示 controller and a high-speed bus interface. 从技术上讲, Thunderbolt combines the PCI Express and 显示Port standards into a single connection, 所以它的连接速度比USB快得多. 

你可以看到 表1, 迅雷1以10Gbps的速度首次亮相, 哪一个迅雷2通过将两个通道合并为一个连接而增加了一倍. 迅雷3 can transfer 40Gbps but this can be limited by cable length and type (see CNET’s excellent article, “USB Type-C和迅雷3:一个端口连接所有的电缆限制,在网上.有限公司/ USBC_TB).

	迅雷1	迅雷2	迅雷3
连接速度	10 Gbit / s	20 Gbit /.  (2频道)	40gbit /s带 .5m电缆
连接器	迷你显示端口	迷你显示端口	C型连接器
支持的其他信号	显示	显示	显示器和USB 3.0

表1. 传输速度，连接器和支持的信号. 

与USB一样，标准与连接器不同. 迅雷1和2使用minid显示 Port连接器, 而迅雷3使用与USB 2相同的C型连接器.0+. 更令人困惑的是，每个迅雷3端口也支持USB 3或USB 3.1, though the reverse is not true; not all USB 3.0 Type C连接器支持Thunderbolt. You see this in Figure 3 showing the four 迅雷3 ports on a new MacBook Pro that supply charging, 显示, Thunderbolt连接和USB 3.1 Gen 2连接. 

图2. The 迅雷3 ports on a new Mac Pro support 显示, power, 迅雷3, and USB 3.1 Gen 2. 

虽然Thunderbolt更快，但USB 3.0 enjoys one benefit that Thunderbolt doesn’t share—the USB Video Class standard (UVC) which simplifies installation and hardware configuration on Windows, Mac, 和Linux计算机. 如果您的USB捕获加密狗是UVC兼容, 大多数高档产品都是这样, you won’t have to install any drivers to get the dongle up and running and you shouldn’t have to configure the hardware for operation in a variety of programs. So, 如果你想使用你的捕捉加密狗和相机作为一个网络摄像头, Skype知道如何配置软件. 如果你在vMix或Wirecast中制作现场活动，同样如此. 与此形成鲜明对比的是, 使用Thunderbolt捕获设备，您必须安装特定于设备的驱动程序, 在某些情况下，它们非常难以启动和运行. 

需要考虑的功能

现在我们已经把摄像机和电脑连接的问题解决了, 让我们确定在评估选项时要考虑的一些特性. 然后我们将回过头来看看Thunderbolt和USB 3.0捕获加密狗要考虑. 

支持的可用性

If you’re using your dongle for mission-critical applications check your support options. 大多数低成本制造商不提供电话支持, 虽然知识库和论坛很有用, 你可以通过电话联系到一位知识渊博的技术人员，这就更好了, 实时聊天紧随其后. 举个例子, Ephipan offers phone and live chat support Monday through Friday from 8:30 - 5:00 EST, 加上电子邮件支持和社区论坛. 

硬件特性

在讨论硬件功能时, you should consider the availability of a signal loop-through function for monitoring or local 显示. Some units also offer an additional audio input to supplement the camera input and/or a headphone jack, 对于某些产品来说，这两个特性都很有价值. You should also verify that the unit is powered via the connector cable to ensure that you don’t need to carry yet another power adapter with you to the event. 

UVC兼容性和软件

显然，如果你买的是USB 3.0捕获产品，您应该检查UVC兼容性.  也就是说, 一些生产者可能希望能够手动控制输入分辨率, 宽高比或色彩空间, 或者类似的参数. 出于这个原因, 一些供应商提供了可以执行这些调整的软件实用程序, 以及方便固件更新和其他维护操作. 如果你是一个新手，检查一下这样一个程序的可用性. 

软件兼容性

If you know which software video mixer you intend to use check their support forums for 信息 about compatibility and reliability before buying any hardware dongles. 经常在亚马逊和B&H包含对这些问题的评论，这些评论也很有价值. 

建设

USB dongles run the gamut from thumbnail-sized plastic devices to solid metal enclosures the size of a deck of cards. If you’ll be using the unit for a single, non-portable application, plastic is probably fine. 如果你要把设备装进工具包，然后去参加多个活动, 坚固的金属外壳可能会在短期内带来好处. 通过嵌入式连接器连接的设备可以节省电缆, 但这些连接可能很脆弱，如果在活动中受到压力，可能会破裂. 

在这方面，当检查B&H和亚马逊, pay attention to comments regarding the stability of operation and how hot the until gets during normal operation. Excessive heat can lead to product failures and make the unit difficult to work with during the event and for immediate packing up. 

迅雷捕获产品

在此背景下，让我们从Thunderbolt开始确定一些候选者. 其中一个成本最低的迅雷3产品是 Blackmagic Design的ultraststudio HD迷你录音机 which supports SDI and analog video inputs with SDI and HDMI outputs ($495 at BHPhotovideo with a 4.5分，10条评论). Blackmagic的ultraststudio 4K Mini(亚马逊上售价995美元), single five-star rating) supports up to 4K SDI and HDMI inputs and outputs with both a 迅雷3 and USB 3.1连接器. 

如果你在找一个多输入的Thunderbolt设备, 看看AJA的IO 4K Plus, which features four SDI inputs and one HDMI input with SDI and HDMI output for monitoring ($2,295 (BHPhotovideo, 2颗五星评价). Another option with Thunderbolt is to connect a Thunderbolt expansion chassis to your notebook via the 迅雷3 connector. These expansion chassis support one or more PCI Express cards that are generally much cheaper than multiple input external Thunderbolt capture devices. 

USB捕获产品

虽然有许多基于usb的捕获加密狗制造商, 其中最熟悉的两个是Epiphan和Magewell. 两者都提供全系列的高清和4K产品，带有HDMI, SDI和DVI输入. 你可以看到Epiphan的AV特征表.io家庭 在这里，以及马格韦尔USB捕获Plus家族的信息 在这里. Both produce premium products for professional streaming applications; you should use the criteria specified above to choose the best product for you.