Benny Tritsch
31 March 2025
When measuring Digital Employee Experience (DEX), capturing high-quality physical and virtual desktop screen videos has become essential for performance test engineers. One of the most effective tools for achieving this is the frame grabber, also known as a screen capture device. Exactly 10 years ago, I wrote my first blog article about frame grabbers - and much of it is still valid today, although the devices have become more modern and screen resolutions higher. Due to the fact that gamers started using frame grabbers for streaming a few years ago, they are now much cheaper. I use a frame grabber as a mandatory component in every EUC Score benchmarking test I run. In this article I answer some questions and provide background information related to frame grabbers.
Technically, you can use your smart phone mounted on a tripod or locally installed screen recording software (such as OBS Studio or FFmpeg) to record physical or virtual desktop sessions on an endpoint device. So, why should performance test engineers turn to frame grabbers to capture their desktops and test applications? Recording local screen videos can be demanding on a computer's CPU and GPU which could affect the recording quality. This could result in low frame rates and screen artifacts appearing in the videos that were not actually there. Frame grabbers offload the video encoding process to a separate device, freeing up the endpoint devices to run virtual desktops and remote applications smoothly without performance hiccups. This means that frame grabbers allow the recording of screen videos in high resolution, often up to 4K, with minimal loss in quality.
For serious performance testers, the dual-PC setup as shown on the right side of the image below is the gold standard. In this configuration, one PC is dedicated to run the virtual desktop client software with (synthetic) user interactions, while the other handles the recording. The frame grabber or screen capture device acts as the bridge between the two, ensuring high-quality video transmission with low latency.
Modern frame grabbers are designed to be user-friendly and with plug-and-play functionality that simplifies the setup process. Virtual desktop test engineers can quickly connect their endpoint devices and start recording without needing extensive technical knowledge. Here is a selection of frame grabbers I currently have in my EUC Score test lab:
While the frame grabbers themselves are quite easy to handle, this is not always the case with video cabling and settings. First of all, knowledge of the common video, connector and cable standards is important, such as High-Definition Multimedia Interface (HDMI), Digital Visual Interface (DVI), and DisplayPort (DP). They all define how digital video and audio data is transmitted from the endpoint device to a computer monitor or in our case to a frame grabber. It is highly recommended to use HDMI 2.0+/2.1+ or DP 1.4/2.0 cables if the maximum resolution is 4K at 60Hz with HDR. The good news is that HDMI is backward compatible with single-link Digital Visual Interface digital video (DVI-D or DVI-I) as well as with DisplayPort and Mini DisplayPort. If you want to use the USB-C port of your endpoint device as video output, make sure there is a symbol of a D (DisplayPort) next to it.
Other video standards relevant in this context are HDR and HDCP. High Dynamic Range (HDR) improves the range of colors and contrast in an image. An HDR display optimizes contrast, brightness, sharpness, and color to enhance realism, clearly differentiating between bright and dark spots in images. Not all frame grabbers support HDR which may negatively affect the video output quality. High-bandwidth Digital Content Protection (HDCP) is a copy protection system to prevent unauthorized transmission of digital audio and video content from a source device to a display or a frame grabber. In most cases, this is not relevant in screen recording scenarios when standard Windows applications are being used.
Due to the compatibility, no signal conversion is required between HDMI, DVI and DisplayPort when using a video port adapter. This makes things easy when connecting the DisplayPort output port of a graphics card to the HDMI input port of the frame grabber. Just use a DisplayPort-to-HDMI adapter and an HDMI cable. There is no loss of video quality if adequate (and sometimes relatively expensive) adapters are used. However, some DVI-D sources use non-standard extensions to output HDMI signals including audio. I can tell you from painful experience that finding the right combination of video output ports, cables and adapters may not be as easy as it seems.
In addition to video port adapters, sometimes video or media splitters are required in a user experience benchmarking setup. A 1x2 splitter enables the video signal from a single video source to be replicated and simultaneously broadcasted both to a display and to a frame grabber. This is a typical setup when the Display Settings in the Windows operating system cannot be used to duplicate the screens across two physical video ports. It is critically important that the video splitter supports the required screen resolution and refresh rate. A good example is the LORYI Display Port to Dual Display Port Splitter Adapter 4K 60Hz.
There are test setups where it is challenging to set up the display(s) in such a way that they show the full desktop in the correct resolution. The root cause may be the EDID information a monitor or the frame grabber sends to a Windows PC and that defines the resolutions shown in the Windows Display Settings. The Extended Display Identification Data (EDID) describes display device capapilities transmitted to a video source, such as a Windows PC or a thin client. Standard EDID resolutions and timings are from 640x480 pixels at 60Hz to 10240x4320 pixels at 120Hz.
Some frame grabbers allow you to set the EDID data and thus predefine the screen resolution. If this isn't the case and the screen resolution is incorrect or unpredictable, using an EDID emulator may be the way to go. Such a video signal passthrough device maintains constant EDID communication with endpoint devices by providing pre-stored EDID information for various signal resolutions. If you want to learn about a popular EDID emulator, check out Dr HDMI 4K.
In summary, frame grabbers offer performance test engineers a powerful solution for capturing high-quality screen videos while minimizing system load and enhancing overall performance. Their versatility and ease of use make them an indispensable tool in the arsenal of any serious performance tester. But sometimes a solid knowledge about video standards and the way device display capabilities are exchanged is required to setup a test environment successfully. If you want to learn more about screen graphics recording, go to Rachel Berry's article Things to know to get started - Recording and Editing Videos or Screen Graphics.
In a follow-up article, I will discuss video recording software that can be used to process and store the high-resolution video data streams provided by frame grabbers. Stay tuned...