What makes a WebM transparent?
A transparent WebM stores color plus per-pixel opacity. The VP9 stream must contain an alpha plane; a normal opaque WebM with black pixels is not transparent and cannot be repaired merely by changing its file extension.
Where should you use it?
- Website hero presenters and product loops
- OBS overlays, alerts and stinger assets
- Chrome and Firefox playback where small delivery files matter
For professional editing, ProRes 4444 is usually a better intermediate because editors handle it more predictably.
A simple HTML setup
Use a video element with muted autoplay and inline playback for decorative loops:
<video autoplay muted loop playsinline src="presenter.webm"></video>
Do not use a checkerboard image as the exported background. The checkerboard belongs only in the preview UI; the file itself should contain transparent pixels.
What about Safari?
Safari compatibility has historically differed from Chrome and Firefox for WebM alpha. A production website should test the current target browser matrix and provide an HEVC-alpha source or another visual fallback where necessary.
Create the right file
In BG Remover Online, choose “Website / OBS” before processing. That choice makes the destination explicit and selects the VP9 alpha output instead of an opaque MP4.