What is the function of upstream keys in video production?

The function of upstream keys in video production primarily involves the use of chroma keying to remove or replace background elements in a live video feed. This technique is widely recognized in broadcasting and film production, allowing for the insertion of different backgrounds or effects behind the subject in real-time.

Upstream keys are applied to the video signal before it is mixed with other sources, enabling the operator to create composite images by layering elements such as graphics or live-action content over a transparent background. This method is especially effective for environments where a green or blue screen is used, as it allows for a seamless integration of the subject with various background settings.

While layering graphics is also a function performed in video production, the specific term "upstream key" is closely aligned with the process of chroma keying and background removal. Other options like controlling video playback pace or managing transitions, although relevant in their own contexts, do not accurately capture the primary role of upstream keys in composite video creation.