Which of the following is NOT a function of the video card?

The correct choice identifies an item that is not a function of the video card, which is primarily responsible for handling tasks related to video processing and output. Video cards are specifically designed to process high volumes of graphical data and render the appropriate signals for display devices.

Mixing video signals pertains to the video card's function of integrating different video inputs into a coherent output. This is crucial for applications requiring multiple sources of video, such as video editing or gaming setups where various scenes or graphics are combined.

Applying signals to the CRT (Cathode Ray Tube) is a traditional function of video cards, particularly relevant in older display technologies. This entails delivering the necessary electrical signals to the display to create images.

Processing video signals is at the core of what video cards do. They take video data from the CPU or memory and convert it into a form that can be displayed on the screen, managing tasks related to rendering images in real time.

Amplifying sound input, however, is primarily the function of sound cards or integrated audio solutions within a computer, which handle audio processing and output. Therefore, it is not a task associated with the video card, making this choice the correct answer.