The problem it solves
A game running on a PC can be copied by software on that same PC. A console, however, runs its own games on its own hardware, and the video it produces goes out through a cable to a screen. A computer has no ordinary way to see that picture. If you want to record or broadcast console gameplay using a computer, you need something that takes the console’s video and delivers it to the computer in a form it can read. That something is a capture card, or capture device.
The same applies to any source that is not running on the capturing machine: a second PC, a camera, or an older machine with video outputs.
The signal chain
The standard arrangement is simple to describe:
- The console sends video and audio out through its output port, typically using a cable of the HDMI type on modern machines.
- The capture card receives that signal on an input.
- The card sends the video to the computer, either through a slot inside the machine or through a cable such as USB.
- Software on the computer reads the video as if it were a camera, and can record it, display it, mix it with other sources, or pass it to an encoder for a live broadcast.
The card does not make the picture; it copies and converts it. The console still does all the game’s processing.
Passthrough
Most capture devices have a second port, called an output or passthrough. The console’s signal goes in, one copy goes to the computer, and another goes straight to a display. This lets the player see the game on a monitor or television without waiting for the computer to process the video.
That matters because capture adds delay. The computer receives, processes and shows the picture some fraction of a second later than the original. Playing from the delayed copy can make a game feel sluggish, so players usually watch the passthrough output and use the computer’s copy for recording or broadcast. The delay in the captured copy reaches viewers, but it does not affect the player’s own input latency when the display is fed by passthrough.
What affects quality
Several factors decide how good a captured picture is:
- Supported resolution and frame rate. Each device handles up to certain video modes. If a console outputs something the device cannot accept, the picture may be limited or may not appear at all. Check the specifications of the particular model against what your console can output.
- Connection to the computer. The video must move from card to computer without exceeding the link’s capacity. This is why many devices specify particular versions of USB or particular slot types. A link that is too slow forces compression or reduced quality.
- Compression inside the device. Some devices compress video before sending it, while others pass it uncompressed. Uncompressed capture generally keeps more detail but needs a faster link and more disk space when recording.
- The computer’s own limits. After capture, the computer typically encodes the video for recording or streaming, and encoding takes processing power. Weak graphics cards or processors can become hardware bottlenecks. The relationship between bitrate and picture quality then applies, as explained in the article on stream bitrate.
- Copy protection. Some video signals are protected by systems intended to stop copying. Whether a particular console or service allows capture of certain content depends on the device and its settings, and sometimes certain screens, such as some menus or media apps, appear blank in a capture. This varies, so check the console’s current documentation.
Internal and external devices
Internal cards sit in a slot inside a desktop PC. They can offer high bandwidth to the computer, and nothing sits on a desk. They are only practical for desktop machines with a free slot, and installing one means opening the case.
External devices connect through a cable, usually USB, and sit beside the console. They work with laptops and desktops alike, are easy to move between machines, and need no installation. Their quality depends on the link and on how the device is built.
Neither type is better in every respect, and the right choice depends on the computer you have and the video modes you need.
Consoles with their own streaming
Many consoles include a built-in feature to broadcast directly to a service, or to save recent clips. This is simpler and requires no extra hardware, but it typically offers less control over layout, sources and quality than a computer running dedicated software. A capture card makes sense when you want to mix in a webcam, overlays, separate audio sources, or a different quality target. The step-by-step process of getting from capture to a viewer’s screen is covered in the explanation of game streaming.
Using a card for other things
The principle is not limited to consoles. A capture device can bring a second computer’s screen into a stream, which is a common way to split the load: one machine plays the game while another handles the broadcast. It can also record older consoles that have analogue video outputs, though this usually needs adapters or a device that accepts those formats, and the results can depend on the display style the old system was designed for, a subject that comes up in discussions of retro gaming and CRT displays.
Practical checklist before buying
- Confirm the maximum resolution and frame rate you need, and that the device supports them.
- Check the connection type on your console and on your computer.
- Look for passthrough if you plan to play while capturing.
- Check software compatibility with your operating system and your recording or streaming program.
- Read current reviews from people using the same console, since behaviour with specific machines can differ.
Specifications and compatibility change as consoles and devices are updated, so treat the current documentation for both the device and your console as the final word.