Capture Cards - CompTIA A+ 220-1101 – 1.17
Let’s have a look at capture cards.
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Capture Cards
A capture card essentially captures a feed of images. A capture card may also capture audio as well; however, technically it does not need to capture audio but most do. Essentially, the way a capture card works is that a video adapter will output a feed of images which goes to the capture card.
Although the term capture card will often be used, a lot of these devices nowadays are external devices and technically not an expansion card. In many cases, these devices will connect to the computer using USB. I personally prefer the external devices, as if something goes wrong, I can disconnect the device and plug it back in, essentially turning it off and on again. With an internal capture card, if something goes wrong, you will need to shut down or reboot the computer which is more of an inconvenience. For this video, I will be referring to all capture devices as video capture cards.
A video feed contains a series of images which results in a lot of data. For this reason, a capture card needs to have hardware real-time encoding, that is, compression to make the data a more manageable size.
Real-time means the capture card needs to output compressed data at the same speed as it is receiving compressed data. Since the compression is done in real-time, the output file tends to be larger than if you don’t use a real-time compressor. Generally, hardware is excellent at compressing video in real-time over what a CPU can achieve; however, it is still limited in the results it can achieve. You can only achieve so much if you want to maintain real-time compression. The amount of video frames you receive must match the number you output, otherwise the capture card will start dropping frames which will cause the video to look glitchy when you play it back.
Once the video is compressed, it is generally sent to a file or to a stream – a file is simply saved to local storage. Generally, it is not recommended to save the file over the network, as if the network has performance problems this may cause frames to be lost.
If you output the data to a stream, this is essentially sending it somewhere else. Nowadays, this often means an online streaming service which will broadcast it to others on the internet.
This basically covers what you need to know for the exam. For the rest of the video, I will have a closer look at capture cards, so you have a better understanding of what is available and what you may need if you decide to purchase one or have to support one.
Passthrough Capture Cards
One of the considerations when purchasing a capture card is if it has passthrough or not. Video capture cards with passthrough have both an input and an output port. Thus, the input will go to your device producing the video you want to capture, for example, a device like a computer or a game console. The output will go to your monitor or TV. Since the video is essentially transferred through unaltered, it is referred to as passthrough. Therefore, the video signal passes through the device and the capture card captures the signal as it goes through it.
The other option is no passthrough. These capture devices only have an input connector. In some cases, this may be all that you need. For example, if you have a video camera that can’t be used as a webcam (however, it does have a video out), you can plug your video camera output into a capture device like this one and it will convert the signal to USB so you can use the video camera as a webcam. In some cases, you may need to capture the video and also display the video on a device like a monitor. If your capture device does not have passthrough, there is another option.
Splitters
If your capture card does not have passthrough you can, in addition, use a splitter. A splitter essentially divides the signal into two. One connection goes to the capture card and the other to your display device.
There are a number of different types of splitters on the market. The most basic, and also cheapest, is a passive splitter. These splitters don’t have power, so they essentially halve the signal strength as it goes through the cable. This makes them less reliable and they won’t support higher resolutions.
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References
“The Official CompTIA A+ Core Study Guide (Exam 220-1101)” page 29
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