Video Capture Dongles Buyers' Guide
Any event captured with a camera can easily be live-streamed. There are myriad technical options for doing this, 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 OBS, vMix, or Wirecast connected to the camera via a capture dongle, which is inexpensive and provides access to titling, transitions, and special effects that add a professional touch.
You’ve got the notebook and software; now you need the dongle, which can cost anywhere from $40 or so to over $700. This buyer’s guide will help guide your purchase decision. Note that the products listed are meant to be representative, 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.
The first obvious concern is whether the unit connects to your camera/output device and notebook. Looking at the source side, of course, you need inputs to match your camera, which typically means either SDI or HDMI. If you want to broadcast from another device, like a computer, you’ll need a dongle that supports VGA or DVI input, though you’re better off acquiring the signal via the Network Device Interface (NDI) or similar protocol that vMix and Wirecast both support.
The computer side has two primary connectors, USB and Thunderbolt. So let’s start with a quick review of USB and Thunderbolt connections and connectors. For perspective, understand that most current capture dongles attempt to transfer uncompressed video into the computer. At 1080p 30fps, that bitrate is about 1.5Gbps, double that for the 60p you’ll want to capture if you’re a gamer. 4K video is 4x both amounts, so about 6Gbps for 4K30p and 12Gbps for 4K60p.
With USB, remember that the standard was created to connect to and supply power to peripherals like keyboards, mice, printers, scanners, and the like. In Figure 1 (from Wikipedia) you see the speeds and connectors of USB 1.0 through USB4. With a top speed of 480Mbps, USB 2.0 clearly can’t transfer uncompressed video which is why all USB 2.0 capture dongles used H.264 compression to transfer the video into the notebook. Even at 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 Type C connector on the bottom of the Figure, you could be connecting to USB 2.0, 3.0, 3.1, 3.2, or USB 4, though USB 2.0 is unlikely. How can you tell which USB standard your computer supports? Check Device Manager on Windows or System Information on a Mac.
Figure 1. USB connection speeds and connectors.
Also, remember that connecting to a faster port doesn’t increase the speed of a USB device. Though you can connect a USB 2.0 capture device to a USB 3.0 connector, the transfer speed is still USB 2.0. Also, while it’s possible to connect multiple dongles to different USB ports on a notebook, if the devices are on the same USB bus, you can still swamp the bus. So, check and make sure that your notebook has two USB busses that you can access before buying multiple dongles.
Understand that even if your notebook has two separate USB 3.0 busses your it may not have sufficient RAM or CPU to mix the incoming feeds. In these cases, consider connecting your cameras to an inexpensive switcher like the Revesun HDMI 2x1 Multi-Viewer with PIP and running the output feed into the capture dongle. You can switch cameras on the switcher, preserve bus bandwidth and CPU cycles and still add titles, slates, and other content to the selected feed via your mixing software.
Where USB was designed to connect to peripherals, Thunderbolt was designed, in part, to displace the Mac MiniDisplay port with a device that could function as both a display controller and a high-speed bus interface. Technically, Thunderbolt combines the PCI Express and DisplayPort standards into a single connection, so it’s a much faster connection than USB.
As you can see in Table 1, Thunderbolt 1 debuted at 10Gbps, which Thunderbolt 2 doubled by combining two channels into a single connection. Thunderbolt 3 can transfer 40Gbps but this can be limited by cable length and type (see CNET’s excellent article, "USB Type-C and Thunderbolt 3: One port to connect them all for cable limitations," at cnet.co/USBC_TB).
20 Gbit/. (2 channels)
40 Gbit/s with .5 m cables
Type C connector
Other signals supported
Display and USB 3.0
Table 1. Transfer speed, connectors, and supported signals.
As with USB, the standard is different than the connector. Thunderbolt 1 and 2 used the MiniDisplay Port connector, while Thunderbolt 3 uses the same Type C connector as USB 2.0+. Adding to the confusion, every Thunderbolt 3 port also supports USB 3 or 3.1, though the reverse is not true; not all USB 3.0 Type C connectors support Thunderbolt. You see this in Figure 3 showing the four Thunderbolt 3 ports on a new MacBook Pro that supply charging, display, Thunderbolt connections and USB 3.1 Gen 2 connectivity.
Figure 2. The Thunderbolt 3 ports on a new Mac Pro support display, power, Thunderbolt 3, and USB 3.1 Gen 2.
While Thunderbolt is faster, 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, and Linux computers. If your USB capture dongle is UVC compatible, and most premium products are, 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, if you want to use your capture dongle and camera as a webcam, Skype knows how to configure the software. Ditto if you’re producing a live event in vMix or Wirecast. In contrast, with Thunderbolt capture devices you’ll have to install device-specific drivers, which in some cases are spectacularly hard to get up and running.
Features to Consider
Now that we have the camera and computer connection covered, let’s identify some features to consider when evaluating your options. Then we’ll circle back and look at Thunderbolt and USB 3.0 capture dongles to consider.
Availability of Support
If you’re using your dongle for mission-critical applications check your support options. Most low-cost manufacturers don’t offer phone support, and while knowledge bases and forums are useful, a knowledgeable technician you can get on the phone is infinitely better, with live chat a close second. As an example, Ephipan offers phone and live chat support Monday through Friday from 8:30 - 5:00 EST, plus email support and a community forum.
While discussing hardware functionality, you should consider the availability of a signal loop-through function for monitoring or local display. Some units also offer an additional audio input to supplement the camera input and/or a headphone jack, both valuable features for some productions. 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 Compatibility and Software
Obviously, if you’re buying a USB 3.0 capture product, you should check for UVC compatibility. That said, some producers may want the ability to manually control the input resolution, aspect ratio or color space, or similar parameters. For this reason, some vendors offer a software utility that can perform these adjustments, as well as facilitate firmware updates and other maintenance operations. If you’re a tweaker, check for the availability of such a program.
If you know which software video mixer you intend to use check their support forums for information about compatibility and reliability before buying any hardware dongles. Often reviews on Amazon and B&H contain comments about these issues which are also valuable.
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. If you’ll be throwing the device into a kit bag and traveling to multiple events, a solid metal enclosure will probably pay dividends in the short term. Devices that attach via embedded connectors save a cable, but these connections can be flimsy and may crack if stressed during the event.
In this regard, when checking reviews on B&H and Amazon, 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.
Thunderbolt Capture Products
With this as background, let’s identify some candidates, starting with Thunderbolt. One of the lowest cost Thunderbolt 3 products is Blackmagic Design’s UltraStudio HD Mini Recorder which supports SDI and analog video inputs with SDI and HDMI outputs ($495 at BHPhotovideo with a 4.5 rating with ten reviews). Blackmagic’s UltraStudio 4K Mini ($995 on Amazon, single five-star rating) supports up to 4K SDI and HDMI inputs and outputs with both a Thunderbolt 3 and USB 3.1 connector.
If you’re looking for a multiple-input Thunderbolt device, check out AJA’s IO 4K Plus, which features four SDI inputs and one HDMI input with SDI and HDMI output for monitoring ($2,295 at BHPhotovideo with 2 five star reviews). Another option with Thunderbolt is to connect a Thunderbolt expansion chassis to your notebook via the Thunderbolt 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 Capture Products
While there are many manufacturers of USB-based capture dongles, two of the most familiar are Epiphan and Magewell. Both offer a full range of HD and 4K products with HDMI, SDI, and DVI inputs. You can see a features table of Epiphan’s AV.io family here, and information on Magewell’s USB Capture Plus family here. Both produce premium products for professional streaming applications; you should use the criteria specified above to choose the best product for you.