Engaging online course lectures using a green screen
Voicing over static slides is inadequate
Fully-online lectures are often just disembodied voice-overs of static slide decks. Not just boring: evacuated of pedagogical context and cues.
Eye contact, hand gestures, & drawing on slides reduces cognitive load
Human interaction enormously increases engagement while writing and drawing provides real-time visual cues for pedagogical focus. Onscreen chat encourages participation: students do not use cameras or microphones.
OBS Studio is free & open source software
The magic is the “video compositing” application called OBS Studio. It allows overlaying various video sources into a single scene, which can be sent to any target (Zoom, Teams) or recorded directly.
Playing meteorologist is surprisingly easy
Coordination between your visual cortex and your motor cortex is incredibly plastic. It takes only a few moments to adjust to gesturing accurately.
Inhabiting figures is the killer feature
The instructor’s face and body provides focus: helpful on text slides, but indispensable for figures. Impossible in person, but easy with this setup!
Inexpensive hardware will suffice
The screenshots above were all produced with a ten-year-old desktop, a ten-year-old tablet and stylus, a pair of discarded monitors, cheap fluorescent lights, miscellaneous cables, two adhesive ceiling hooks, and a curtain rod and a few dollars of green fabric.
Step-by-step instructions
Hardware
- a laptop or desktop computer, preferably with at least 16GB
- a webcam
- lots of light sources (the chroma key filter will struggle in low light, and you will need more light than you might expect)
- a green background (e.g. a green cotton sheet over a curtain rod mounted to wall or ceiling via removable adhesive hooks
- optional tablet input: connect tablet HDMI video output to a HDMI-to-USB capture card to the computer
- optional extra monitors connected to computer
Software
Download OBS Studio and install it onto the computer. For a minimal configuration, create a Scene in OBS Studio with the following Sources:
| SOURCE TYPE | SOURCE | |
|---|---|---|
| top layer | Video Capture Device | webcam input |
| Window Capture | e.g. slides app | |
| middle layers | Window Capture | e.g. web browser |
| Video Capture Device | tablet HDMI-to-USB capture | |
| bottom layer | Image | neutral background image |
| Media Source | neutral video loop |
Finally, configure the webcam with a chroma key filter to remove the green screen. Select the webcam Source and add a Filter: “Effect Filters” “Chroma Key.” Start with the default settings and adjust as needed.