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Choosing a Capture Card for Multicamera Live Production
- Categorized in: Live Video Production
You’ve decided to create your own station for mixing live events with a software program like Telestream Wirecast, Livestream Studio, StudioCoast vMix, CombiTech VidBlaster or Splitmedia Labs XSplit. You’ve selected the mixing software you plan to use, you’ve spec’d out the computer, and now you need a capture device to input the feeds for mixing.
To choose the best card, you should pursue multi-part analysis. First, you should make sure that all candidate capture devices work well with your mixing software, which sounds simple, but has multiple layers and some subtleties. Then, you should identify the features that you absolutely require, such as the number of input channels and their formats, or the availability of ISO recording, and eliminate any candidates that don’t supply them. Then you need to focus on more quality and performance features, such as onboard scaling and deinterlacing, and identify preference items, such as whether you want a breakout box to conveniently access all of your connectors.
Finally, you need to scrutinize the message boards of the mixing software vendor that you’ve selected and the capture card vendor to identify compatibility, stability, or similar issues, and to gauge vendor responsiveness to problems or feature requests. Plus you need to scan reviews on sites such as B&H and Amazon to get the opinions of actual buyers. In this article, I’ll get you up to speed on what features to look for, but you’re going to have to carry the load on the critical subjective items.
Does It Work With Your Mixing Software?
The first step is to check the website of your mixing software provider to identify supported capture products. Most vendors support the widest possible range of products, but there’s often a hierarchy. For example, Telestream keeps a list of Wirecast-compatible capture cards that their technical staff supports, and a separate list where the manufacturers have tested compatibility; obviously, you’ll be better support with a board in the first class.
Beyond this, try to learn which capture products are used by turnkey system designers who build systems around the same software. For example, 1 Beyond produces portable Wirecast systems usually built around the Matrox VS4. Livestream builds all of its systems around Blackmagic Design hardware, while vMix seems to favor AJA capture gear. If I were buying a capture device to run these programs, such integrations would carry a lot of weight.
Does it Run on Your Operating System?
Nothing exotic here; just including the point for completeness. Of course, if you’re considering mixing with a system that uses Windows 10, make sure your capture device supports the new before buying (Figure 1, below).
Figure 1. The Blackmagic DeckLink 4K Extreme 12G supports Blackmagic 4K cameras, with an inexpensive adapter for supporting Quad-SDI input.
Does it Support Your Required Inputs?
This is the point where you sit down and list all formats that you need the capture device to support. For some buyers, that’s simple: Perhaps you’re buying a system to support a single set of consistent inputs, such as four HD-SDI or HDMI cameras. For others, it’s more complex: Either you’re building a general-purpose system to work with multiple camera types, or you need compatibility with a range of inputs, not simply cameras, such as DVI or VGA for lecture capture. Or, perhaps you need a capture card that will support 4K input as well as HD-SDI. List all the formats your system needs to support and buy capture hardware that supports them.
There are multiple fine points to consider for many of these inputs. For example, if you need the ability to customize the input resolution of your DVI sources, make sure that your capture device lets you apply custom extended display identification data (EDID) profiles, a feature of several Epiphan capture devices. If you need support for a range of consumer formats, consider a product such as the AverMedia DarkCrystal 750, an external USB-based capture box that supports HDMI input and component input.
If you’re buying a card for 4K capture, note that there are multiple standards in play. Some 4K cameras support Quad-Link HD-SDI output, which transmits the 4K signal as four 1080p HD-SDI signals over four cables, allowing many boards with four HD-SDI inputs, such as the AJA Kona 4 or the Ospret 845e (Figure 2, below), to also capture 4K input. Some cameras output via HDMI 1.4, which can be captured with less expensive cards, such as the Magewell XI100DE-HDMI-4K, though the slower speed of HDMI 1.4 may limit capture frame rate or color depth.
Figure 2. The Osprey 845e has 4 HD-SDI inputs, with ProcAmp controls and onboard scaling and deinterlacing.
Blackmagic Design cameras output in 6G or 12G, which is primarily supported by Blackmagic Design capture cards, such as the DeckLink 4K Extreme 12G, to which you can add Quad Link capture via the DeckLink 4K Extreme 12G-Quad SD adapter card. The 4K market is far from standardized, so if you’re buying a card for 4K production, spend extra time on message boards and product forums to find known-compatible products.
Be sure to include audio on your list. If all of your audio will be input with the video, that’s easy; if you need to support inputs from other sources, you may need to buy an audio capture board as well. Some vendors, such as Osprey and Epiphan, have separate products or adapters that enable extra audio inputs, which obviously should work well with their respective capture cards. Others focus solely on video capture, and recommend third-party cards for audio capture. In the latter case, you should perform extra due diligence to find cards that function well with your video capture board.
While on the subject of input, check whether a capture card can auto-sense the video input or whether you have to set it manually. Unless you consistently work with the same input formats and configurations, auto-sense is much more convenient and will save you time and frustration each time you try to set up the system. If you’ll be working with different inputs from different cameras, make sure the capture board can handle this; some require the same incoming format for all inputs.
If you currently have HDMI or analog gear, but plan on upgrading to HD-SDI in the near term, consider buying an HD-SDI capture card and separate devices to convert these inputs to HD-SDI. Both AJA and Blackmagic Design have full lines of converter boxes for this and other similar conversions.
Scaling and Deinterlacing and Other Adjustments
If you need to save ISO feeds from your incoming sources, you’ll want to capture at full resolution. Otherwise, with both internal and external capture devices, you may want to scale the incoming video to the output resolution of your capture device to improve scaling quality and save CPU cycles on the host computer. Not all products can perform this scaling, making on-board scaling and deinterlacing features worth checking for.
Also check if the capture device provides video adjustment features such as a ProcAmp with scopes, like those available on Osprey video cards. One aspect of streaming live is that you can’t fix it in post, so the ability to adjust video characteristics such as contrast and saturation can be a valuable adjunct to the typical exposure and color adjustments found on most camcorders.
Does it Provide the Required Outputs?
For many streaming producers, the sole output will be a streaming signal to one or more services. However, if you’re broadcasting in an arena or similar venue, you may also need HD-SDI/or HDMI output of the program stream to feed a monitor or IMAG system. Many capture cards are input only, so if you need HD-SDI or HDMI out, make sure it’s supported, either directly, or via a separate add-in card. To be perfectly clear, note that you need the full output of the program stream, not simply a passthrough of one of the input channels, which many cards provide.
Another common requirement is ISO recording, which stores the individual inputs or the program feed to hard disk where it can easily be edited or uploaded to YouTube or other sites. Note that Wirecast and other programs can store a lower-resolution encoded copy of the program stream, but this is different from true ISO recording, which uses hardware processing on a card such as the Matrox VS4 (Figure 3, below) to store broadcast-quality output ready for further processing.
Figure 3. The Matrox VS4 is used in many Wirecast-based turnkey systems because of its performance and ISO recording capabilities.
How Do You Achieve the Required Density?
Keep in mind that density, or the number of supported inputs, has two discrete components: enough ports to physically connect the required inputs, and sufficient CPU horsepower to mix and compress the incoming streams without dropping frames. In this regard, while you may be able to input three 1080p signals into a MacBook Air via its two USB 3.0 ports and single Thunderbolt port, that doesn’t mean that the 1.6 GHz dual-core Intel Core i5 CPU can mix the feeds and produce the required streaming output without dropping frames.
On the other hand, a 15" MacBook Pro with a 2.6GHz quad-core Intel Core i7 CPU just might do the trick, as Imry Halevi, Harvard’s Director of Multiple Production for the Department of Athletics, explains in his blog post High Definition, Three Camera Inputs, One Laptop, $3,500. In his setup, Halevi plugged two Blackmagic Design Mini Recorders ($149) into the available Thunderbolt ports, and a Blackmagic Intensity Shuttle USB 3.0 ( $199) into one of the MacBook Pro’s USB ports, for input.
At the risk of sounding politically incorrect, as Halevi’s post suggests, there are many ways to skin a cat. Though Blackmagic and AJA seem to be the only vendors with Thunderbolt capture dongles, there are multiple suppliers of inexpensive single- or dual-port USB capture, including Magewell, Epiphan, and AverMedia. Those seeking higher-end capabilities are a higher price point could substitute a single AJA Io 4K (Figure 4, below $1,995) to enable four HD-SDI inputs, HDMI input, with superior monitoring and output capabilities as well as 4K support in and out.
Figure 4. Connections available on the AJA Io 4K, a four-input external Thunderbolt capture device
Internal cards are subject to the same CPU caveats. Just because you can install an 8-port board into a computer doesn’t mean the computer will be able to successfully mix the streams. If your system is powerful enough, you can find a variety of single-, dual-, quad-, and eight-input cards, and if you have enough slots, you can install multiple capture boards into a single computer to achieve the required density. Producers who dislike the mini HD-SDI connectors used on most 8-port cards can install two 4-input cards to reach the same number of inputs.
Warranty and Support
Warranties for most products in this class range from 1–3 years; while three years sounds much better, the reality of hardware components is that most failures occur early, and otherwise the products tend to live forever. More important than warranty period is the availability of technical support, which you’ll likely need during the install process, and then later should a failure occur. Not all vendors offer U.S. local phone support, which is a big negative in my view.
Try to ascertain if the company will hot-swap for defective products under warranty, and send you a replacement product without first receiving your unit, which will accelerate your receiving the replacement by 2–5 days. Most will, but some require a credit card for the service.
As mentioned earlier in this article, be sure to check user forums and similar venues to see how quickly the company responds to user issues and feature requests. A vibrant forum and user community speaks well for the vendors and the viability of their products. The diversity of video capture programs, host computers, and use cases ensures that problems will always appear; it’s not the problem that’s significant but how quickly the vendor moves to resolve it. Finally, no matter where you actually buy the products you’re considering, check reviews on B&H and Amazon before pulling the trigger.
With this, let’s move to issues to consider for external and internal products.
If you’re fortunate enough to have both USB 3.0 and Thunderbolt ports available, USB 3.0 should suffice for up to two HD streams, particularly if you throttle the input down to 720p before inputting that into your video mixing software. Most solutions are single input, though Magewell has an interesting product called the XI200XUSB that supports two HDMI, VGA, or component inputs. If you need more than two inputs from a single port, however, Thunderbolt is a better solution.
If you’re buying a capture product for a USB 3.0 port, note that there are two classes of products: UVC (for USB video class) products that install on Windows, Mac, and Linux computers without a driver; and products that require a driver. Essentially, the tradeoff is simplicity versus configurability. The first class works well if you’re capturing standard signals like HD-SDI or HDMI, but if you’re capturing non-standard signals like VGA input from a notebook, or a feed from a document camera, you may need the configurability offered by a driver-based product to customize the feed. In essence, this is the difference between Epiphan’s AV.io (Figure 5, below), a UVC device that costs $349; and the DVI2USB 3.0, which includes drivers and costs $699.
Figure 5. The Epipan AV.io, a simple-to-use UVC USB dongle with DVI, HDMI, or DVI input
As capture devices go, USB seems to be the most finicky connection, so perform extra due diligence on user forums and Amazon and B&H before buying any USB product.
There are a number of considerations unique to internal cards which I’ll run through quickly.
First, make sure any card that you consider can fit into your computer, which is a particular issue if you’re buying a small case for portability. Some small cases require half-height cards; if you’re working with one, you should know that AJA has a line of cards on their developer program which comes in full and half-height models.
Beyond height, keep in mind that your computer will have multiple PCI Express slots which can be 1-, 4-, 8-, and 16-lane slots. Capture cards are built for these different slots, with single input cards usually having one lane, with higher-density cards now requiring up to eight lanes, with 16-lane capture cards coming. As you would expect, single-lane cards can fit in any slot, but 8-lane cards can only fit into 8- or 16-lane slots. If you’re buying a high-density capture card, make sure you have an open slot to insert it into.
Finally, if you don’t take great pleasure from crawling behind your computer to connect and disconnect audio and video cables, consider choosing a capture card with a breakout box, like all KONA capture cards from AJA. The knees on your jeans, and the back of your head—two frequent casualties of connecting cables behind computers on your floor—will definitely thank you.
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