EMZETT.Capture Card
In short: An expansion card or external device that captures a video/audio signal (e.g. from HDMI) and makes it available to the PC as a data stream.
In more detail: Typical use: a game console or camera is connected to the capture card via HDMI, the PC receives the signal like a normal video source and can record or livestream it. Capture cards come as an internal PCIe card or as an external USB device.
In Depth
Why special hardware is needed
The reason a capture card is needed at all: a normal PC display output (e.g. DisplayPort or HDMI) is designed purely as an output, not an input — a graphics card can send a video signal, but without extra hardware can’t receive and process an external video signal, since it lacks the receiving and digitising electronics needed for that. The capture card handles exactly this translation: it takes in an input signal (say from a game console, a second camera or an old VCR) and makes it available to the PC via USB or PCIe as a perfectly ordinary “webcam-like” video source, which any recording or streaming software (OBS, Discord, Zoom) can use directly without special handling.
Internal vs. external capture cards
Internal PCIe capture cards (installed as an expansion card inside the case) usually offer the lowest latency and highest quality, since data transfer runs directly over the fast, lightly loaded internal PCIe bus. External USB devices (connected via a USB cable) are considerably more flexible to use between several computers, but are subject to the shared bandwidth and higher latency of USB compared to PCIe, which can become noticeable with very high-resolution signals (4K at a high frame rate).
Important specs
Important specs when buying are the maximum supported resolution and frame rate at the input (e.g. 4K at 60 FPS, or Full HD at up to 240 FPS for very smooth game recordings), whether the signal is looped through losslessly (pass-through — the incoming signal is simultaneously forwarded to your own monitor with minimal extra delay, so you can, for example, play with low latency on your own monitor while recording in parallel, without being affected by the recording delay), as well as whether compression happens in hardware on the card itself (spares the PC’s CPU) or is left entirely to the PC (more flexibility in compression settings, but higher system load).
Typical use cases
Besides the obvious use case (recording/streaming console gameplay), capture cards are also used professionally: for signal monitoring in video production, to feed several camera signals into streaming software at once (multi-cam setups), or to digitise older analogue video sources, for which special capture cards with analogue inputs (composite, S-Video) are needed instead of the usual HDMI variants.
HDCP as a hurdle
A practical problem with many consoles and streaming devices is HDCP (High-bandwidth Digital Content Protection) — a copy-protection mechanism that encrypts a video signal and only lets it through to “authorised” output devices. A capture card that isn’t allowed to actively decrypt the HDCP signal (which is legally and technically demanding) often shows only a black screen or an error message instead of the actual signal for protected content — a common stumbling block when recording certain console games or streaming services, affecting many cheap capture cards, while more expensive models specifically “pass through” the signal without themselves violating the copy protection.
Driverless vs. driver-based detection
Many modern external capture cards use the UVC standard (USB Video Class), which lets them be automatically recognised by the operating system as a generic webcam, without needing their own driver installation — practical for immediate use, but often with a limited feature set (e.g. no adjustment of recording settings via manufacturer software). Higher-quality internal PCIe cards, by contrast, almost always need special drivers and bundled software to access their full range of capabilities at all (e.g. hardware encoding, several simultaneous inputs).