CasparCG

JohnCG uses CasparCG, an open-ource character-generator, as its rendering engine. It can play out media-files and programmable HTML-files called templates.

Terminology

channels

Multiple independant compositions can be created simultaneously and are called channels.

layers

Each channel has infinite layers that are composed on top of each other based on their transparency.

producers

Producers render the image and audio displayed in the individual channels.
Producers are for example:

ffmpeg-input
media-items
HTML-templates
video-input from a Blackmagic DeckLink card
solid colors
another producer
NDI

mixer

Mixers modify the media in a layer.
Some mixers are for example:

position
scale
rotation
opacity
brightness
saturation
contrast
blend-mode
clip (masking)
volume

consumer

Consumers output the composed signal of a channel to different interfaces.
Those are for example:

Blackmagic DeckLink cards
ffmpeg
NDI
screen: a windowed or fullscreen window in the os