Short answer: add a transparent WebM (VP9 alpha) as a Media Source for overlays, or pick it as the video file of a Stinger transition. Do not add a chroma key filter.

As an overlay: Media Source

  1. In your scene, click + → Media Source.
  2. Choose your transparent .webm (or a ProRes 4444 .mov).
  3. Tick Loop for a looping presenter or alert, and position it over your scene.

The transparent areas show whatever is underneath. There is nothing to key out, so leave the Chroma Key filter off—it only eats into hair and soft edges.

As a transition: Stinger

In Scene Transitions, add a Stinger, select the WebM as its video file and set the transition point to the moment the video fully covers the screen. A stinger with alpha lets your scenes show through around the animation.

If the background shows as black

  • Check the file really has alpha (see how to check). An MP4 almost never does.
  • Update OBS: transparent WebM playback relies on its media decoding, and old versions handled alpha less reliably.
  • If you converted the file yourself, make sure the encoder was given -pix_fmt yuva420p and the WebM carries the tag ALPHA_MODE=1 (FFprobe still lists its pixel format as yuv420p—that is normal).

Making the file

Remove the background from a webcam clip or a presenter recording with our video background remover and download the transparent WebM—it is made for exactly this. For an animation exported as PNG frames, use the free PNG sequence to WebM converter.