How Do Capture Cards Work?

To maintain FPS and stream quality, capture cards are almost always a necessity for streaming. While widely known as a product, the specifics of how capture cards work can be a mystery. While they appear to be a complicated piece of technology, these cards are actually more simple than you might think. 

Understanding how capture cards work requires a basic understanding of how video game graphics work. Games render their animation in real-time, by sending signals to the GPU which then turn those signals into the visuals you see on your screen. These real-time visuals differ from the pre-rendered files that are used for most videos. As most modern games are generally GPU intensive, your GPU can struggle to both render your game graphics and also encode them into video footage for streaming. This is where capture cards come into play.

Internal vs External Capture Cards

There are two types of capture cards, internal and external. While they have different methods of installation, the basics of how they work are largely the same. An internal capture card will be installed directly into the computer, while an external card will be connected through USB or other similar means. 

An internal card simply needs to be installed in the PC you are playing games on, and the video and audio signals will be sent directly from the card to your streaming PC for encoding. For PC’s, the internal card is installed directly onto the motherboard of the Gaming PC via one of the PCI slots. 

An external card connects to the device you are using to play games on, and the device you are going to record/stream the footage on. 

How the Card Works

The capture card works as a sort of “bridge” between whatever device you are gaming on and the computer used to upload the footage. The gaming device can range from another PC to consoles like an Xbox One or even a Switch. 

Due to the density of the data, most capture cards will end up creating a small amount of lag between the gaming device and streaming device. Better quality capture cards will reduce this lag considerably. If you’re simply saving this video file for later use, such as uploading gameplay footage to YouTube, this footage will be stored on the streaming PC.

The resulting file will likely be encoded in an H.264 format, which is the standard format used for almost all video files. If you’re going to be streaming the footage through Twitch, Mixer, or other streaming sites, the video file will be encoded and sent directly out to your viewers. 

It is important to note that the capture card does NOT do the encoding itself; that will still be done by your streaming PC. A common misconception is that capture cards will both capture and then encode the video files, which would lead to some offloading of processing from your computer to the capture card. Many consumers tend to be disappointed when a capture card does not end up lightening the processing load of their streaming PC, but this is simply not something most capture cards are capable of doing. 

Some capture cards are capable of performing some encoding, but this is typically a process for only the highest end cards. Throughout the whole transfer process, most capture cards will do little more than transmit data from one device to another. 

Not all capture cards are created equal, so it’s extremely important to do your research on top capture cards. Some capture cards aren’t able to simultaneously receive and send out data, making streaming impossible. These capture cards will still be able to store the recorded files for use onto an external drive, making them work fine for recording gameplay footage for reviews or Let’s Plays

No matter how you plan to use a capture card, it should be able to get you your footage cleanly and easily. If you’re planning on entering the world of streaming, or just want to learn more about it, understanding the mechanics of these important devices can prove invaluable.