user11923: To fully understand the how it works: you pick any device with HDMI output (let's say GoPro to reduce the variations) and you'll need a capture card for retreaving the data as multimedia signal. Please correct me where I'm wrong:

a digital signal is coming from the GoPro, why can't you process that signal completely trough software? What's the hardware for?
is the hardware purely for transcoding (and providing an input connector) or there is something else that I'm missing?


user14256: EVERY place the computer CPU connects to the rest of the world requires an interface (hardware and software) of some kind. There is a very complex interface to get the data out of the computer and on to the screen where you are reading these words. And another interface to capture the key-strokes and convert them into characters entering the computer. And another interface for the speakers and for the microphone, and for the mouse, and for the WiFi and for the Ethernet and for the hard drive, etc. etc. etc.
So it should be no surprise that it takes some kind of interface to get the digital video stream of ones and zeros and gets them into the computer, also.  Back years ago, the screen interface was a separate card, and the audio (speaker and microphone) was a separate card. And the USB to the mouse and keyboard was a separate card. But modern computers have integrated all of those INTO the computer which apparently makes you think that they don't exist. 
But those interfaces are all required to get things in and out of the computer, and video is just another kind of signal that needs an interface (both hardware and software).  But since most people don't need to ingest video, few (if any?) computers include a video input interface, so you must use a separate (internal or external) gadget to import video into your computer.
Yes, the hardware is to provide a place to plug in the video signal, but there is a requirement for software also. To "bundle" the video data into a form that the operating system and the video application can understand.

11923: <p>To fully understand the how it works: you pick any device with HDMI output (let's say GoPro to reduce the variations) and you'll need a capture card for retreaving the data as multimedia signal. Please correct me where I'm wrong:</p>

<ul>
<li>a digital signal is coming from the GoPro, why can't you process that signal completely trough software? What's the hardware for?</li>
<li>is the hardware purely for transcoding (and providing an input connector) or there is something else that I'm missing?</li>
</ul>
 14256: <p>EVERY place the computer CPU connects to the rest of the world requires an interface (hardware and software) of some kind. There is a very complex interface to get the data out of the computer and on to the screen where you are reading these words. And another interface to capture the key-strokes and convert them into characters entering the computer. And another interface for the speakers and for the microphone, and for the mouse, and for the WiFi and for the Ethernet and for the hard drive, etc. etc. etc.</p>

<p>So it should be no surprise that it takes some kind of interface to get the digital video stream of ones and zeros and gets them into the computer, also.  Back years ago, the screen interface was a separate card, and the audio (speaker and microphone) was a separate card. And the USB to the mouse and keyboard was a separate card. But modern computers have integrated all of those INTO the computer which apparently makes you think that they don't exist. </p>

<p>But those interfaces are all required to get things in and out of the computer, and video is just another kind of signal that needs an interface (both hardware and software).  But since most people don't need to ingest video, few (if any?) computers include a video input interface, so you must use a separate (internal or external) gadget to import video into your computer.</p>

<p>Yes, the hardware is to provide a place to plug in the video signal, but there is a requirement for software also. To "bundle" the video data into a form that the operating system and the video application can understand.</p>
