Benchmarking PCs, Capture Cards, and Software Mixers for HD Capture and Streaming

Desktop Testing

Though notebooks have obvious appeal for mobile producers, desktops are cheaper, particularly if you already have them around. They’re as convenient as a notebook if you produce from a single location. The first set of tests I ran was to determine if a circa-2011 HP Z600 workstation with two 2.66GHz Intel Xeon CPUs, each with four cores (eight with HTT), can serve as an adequate platform for live event production. I tested with two cards from Osprey Video, the dual HDMI input Osprey 821e and the Quad HD-SDI (or dual input 3G SDI or DVB-ASI) Osprey 845e. I tested with Wirecast and vMix, but not OBS, assuming that a multiple-camera event producer wouldn’t use shareware.

It seems that every time you install a capture card, you learn a new lesson, and so it was with the Osprey 821e. Specifically, despite being a four-lane PCI Express (PCIe x4) card that could physically fit into one of the four-lane PCIe ports on the Z600 motherboard, the 821e needed the bandwidth available only in a PCIe x16 slot (Figure 4, below). I discovered this after installing the board into an x4 slot and spying intermittent color bars in the mixer’s preview window. I called the always-helpful Osprey tech support line, and the first question the tech asked was in which slot I installed the card.

Figure 4. Even though the Osprey 821e could fit into a PCIe x4 slot, it needed the bandwidth available from a PCI x16 slot. Click the image to see it at full size.

When I told him it was the PCIe x4 slot, he suggested that I install it into the PCIe x16 slot instead, which resolved the problem. This brings up two key points. First, if you’re attempting to convert an existing workstation into a live capture station, make sure it has a free PCIe x16 slot, particularly for a video capture card with two or more inputs. Second, as you’ll see with the four-port Osprey 845e card, a live capture station needs both a fast CPU and a speedy bus.

Dual HDMI Inputs (Osprey 821e)

Once I had the system up and running, performance with dual HDMI capture proved more than adequate, particularly with the vMix software. As you can see in Figure 5 (below), the system easily processed a 720p live stream plus an MP4 archive, plus all the other tests we threw at it. With Wirecast, the results were about 10 percentage points higher in all tests save x264, where CPU utilization pushed to about 50%. Quick Sync is not an option for the older Xeons on the Z600.

Figure 5. CPU utilization for vMix on an HP Z600 with two 2.66GHz quad-core Xeons. Click the image to see it at full size.

Unfortunately, the system peaked with the dual HDMI input card and proved inadequate for the quad HD-SDI 845e card. Interestingly, it wasn’t CPU utilization that disqualified the unit—it was bus throughput. I ran the same tests with the 845e as I did with the 821e, and CPU utilization for both programs was very similar. However, periodically during the production, color bars would replace the video in the preview and output windows, indicating that all video data was not getting through.

While the CPU power may be sufficient on these older systems, you’ll need the bus speeds available on newer systems to support four-channel input cards. Would two dual-input HD-SDI cards have worked? Interesting question: That’s definitely an option I would explore if I had to make the Z600 work.

Matrox VS4 and an i7-Based System

Over the last few generations of processors and motherboard chipsets, bus and memory throughput has improved along with the number and speed of CPU cores. This takes us to the last system that we tested: a custom-built i7-based system supplied by Matrox with its VS4 Quad HD capture card. Specifically, the computer was powered by a 3.4GHz i7-4770 CPU with 16GB of RAM and an Nvidia Quadro K620 graphics card running Windows 7 with 16GB RAM. The chipset was an Intel Z87, which falls into the Haswell family.

The VS4 is a quad HD-SDI capture device with hardware ISO recording capabilities that makes it efficient to capture ISO streams from each of your four source devices. In this series of tests, shown for vMix in Figure 6 (below), both software programs performed well, though Wirecast used about 5 percentage points more CPU than vMix in most tests.

Figure 6. CPU utilization for vMix on a generic i7-based system and the Matrox VS4

As you can see in Figure 6, with the i7-based system, vMix was able to stream to Facebook Live and capture four ISO streams in MPEG-2 I-frame format while staying well below 60%. Adding a live stream to Ustream boosted CPU to almost 70%, though ISO files captured by both programs were free of dropped frames.

The other point of Matrox’s hardware-based ISO recording is that it produced better quality than the equivalent MJPEG-based QuickTime output. You can see this in Figure 7 (below), which shows Matrox on the left and QuickTime footage on the right. You can certainly correct some of the dinginess on the right with brightness and contrast adjustments, but the Matrox frame is much sharper as well. If ISO recording is important to you, you should strongly consider buying a board with hardware-based ISO output.

Figure 7. Matrox’s hardware-based ISO output was superior to Motion JPEG-based QuickTime.

Summing Up

You may be wondering, “Why didn’t you try the quad-input Osprey 845e card on the i7-based system?” Well, I did, but the system didn’t recognize the card. This happens sometimes, according to Osprey’s tech support staff, which is a good intro into our final conclusions.

First, not all capture cards work with all systems. If you’re buying a capture device for an existing computer or notebook, make sure it’s returnable because there’s a good chance it won’t work. If you’re buying a new computer to convert to a live switching station, you should strongly consider a prepackaged system. Telestream just entered this market with multiple systems under the Wirecast Gear label, while vMix has offered turnkey systems for a while. You can also buy from third parties such as 1 Beyond or Paladin, and Osprey Video also offers base systems you can buy for guaranteed compatibility, performance, and stability.

Along the same lines, recognize that not all capture cards work equally well with all software video mixers. All capture products have a generic DirectShow interface (or the Mac equivalent) that software vendors can use to work with the device. However, they also usually offer software development kits (SDKs) for improved performance and more stable operation. It’s hard to tell which level of support the software video mixer affords each capture device, but it’s a safe bet that if the vendor offers an integrated system, the software mixer supports the capture card’s SDK directly. This is another reason to buy a turnkey system.

If you’re looking for a notebook-based system, you’ve seen that the different software programs consume varying levels of CPU. You’re best off experimenting with multiple programs to find the best mix of features and performance. This is also true if you’re building your own desktop system from an existing workstation or computer. Beyond producing and watching live streams, be sure to check your archived streams for drop frames.

Finally, if you’re building your own system from a notebook or desktop, note that some problems don’t appear until 20–30 minutes into a production, or even longer, so you should test the system for the expected duration of your longest planned live production. Remember to test with footage similar to the actual live event, since a system that performs well when encoding a static scene may fail when encoding the actual soccer game it was designed to produce.