How to Make a Transparent VTuber Overlay with WebM Alpha

To make a transparent VTuber overlay without a green screen, export the avatar clip as VP9 WebM with an alpha channel (yuva420p), then add it in OBS as a Media Source. Do not add a Chroma Key filter—the transparency is already in the file. Use ProRes 4444 only as an editing master (ExportAlpha ProRes clips are limited to 8 seconds); use WebM for longer loops up to 60 seconds. ExportAlpha processes an uploaded file—it is not a live face-tracking plugin or virtual camera.

Updated October 30, 2026

Spec box

≤60s overlay ≈ Quick $6.99

What “transparent VTuber overlay” means

In this guide, a transparent VTuber overlay is a pre-rendered video file of an avatar, mascot, Live2D capture, or pngtuber-style animation that already stores per-pixel transparency. You place that file over gameplay or a camera scene in OBS. The holes in the frame are real alpha data—not a green box you key again on stream.

That is different from live face-tracking VTubing, where software drives a model from a webcam in real time. ExportAlpha does not do live webcam keying, does not install as an OBS plugin, and does not replace VTube Studio–class tracking tools. If you need a live tracked model during the stream, use the tracking stack you already have; use this page when you need a file-based corner loop, bumper, or short reaction clip with true alpha.

WebM VP9 alpha vs green-screen MP4

Everyday H.264 MP4 cannot store transparency. If your avatar export is an opaque MP4 with a desk, room, or editor background, you need background removal (or a flat-color key) before the WebM encode. For the key-vs-AI decision tree, see Green screen to transparent WebM.

Who this guide is for

• You already have a short animation or capture and need a looping corner overlay, lower-third-style bumper, or intro clip in OBS / Twitch.
• Your capture still shows a desk, room, or solid editor background and you need true alpha, not a green box to key again.
• You are not looking for a live face-track plugin or a virtual webcam that keys during the stream.

Overlay vs stinger vs live camera

Path A — Filmed or screen-captured model

1. Capture a short clip of your avatar. A simple, contrasting background helps when you can get one. Green screen is optional; uneven real rooms usually need AI matting instead of a single chroma key.
2. Keep the clip ≤ 60 seconds if you want one WebM from ExportAlpha. Longer performances: cut into segments.
3. Upload at exportalpha.com, wait for processing, download Transparent WebM.
4. In OBS: Sources → Add → Media Source → browse to the .webm → enable Loop if it should repeat → leave chroma key off.
5. Place the Media Source above game capture / camera in the source list so it is not covered.

Path B — Already-transparent motion graphic

If a motion tool already exported ProRes 4444 (or another alpha master), skip background removal. Prefer VP9 WebM for a lighter OBS overlay; ExportAlpha ProRes is capped at 8 seconds. Format matrix: Which formats support transparency?.

Path C — Live2D / pngtuber / desktop avatar apps

Many apps preview with transparency on a checkerboard, then record or export an opaque MP4. Treat that export like Path A: remove the leftover background, then write WebM with alpha. Exact menu names differ by app and version—verify them in your software. This page does not invent click paths for third-party tools.

No green screen path

You do not need a physical green screen if:

1. You can remove a real background with AI matting that writes alpha, then export WebM; or
2. Your motion tool already wrote an alpha master (ProRes 4444 / similar).

You do need either a flat keyable color or AI removal if the capture is an opaque MP4 with a busy room. Green screen is a convenience for keying—not a requirement for WebM alpha delivery.

Step-by-step OBS Media Source

1. Use Media Source, not a window capture of a player that paints black.
2. Confirm the file is VP9 WebM with alpha, not everyday H.264 MP4.
3. Loop on for repeating overlays; off for one-shots (alerts belong on the stream alerts guide).
4. Do not stack Chroma Key on a file that already has alpha.
5. Optional: OBS documents Apply alpha in linear space on Media Source—test both states if edges look wrong (detail on the OBS guide).
6. If you see a black box, read Why transparent video turns black.

Loop vs one-shot reactions

• Looping presence overlay (always-on corner mascot): Loop on.
• One-shot reaction (wave, hype clip): Loop off; trigger visibility or use the alerts pattern (Restart when active).
• Do not confuse overlays with stingers—stingers are scene transitions, covered separately.

Limits of pre-rendered overlays

A pre-rendered WebM cannot lip-sync to live audio, follow unrecorded head poses, or replace live tracking. Cut longer performances into ≤60s segments for ExportAlpha’s WebM path. Failed jobs refund credits. Job files are deleted 7 days after processing finishes — see Sources.

When ExportAlpha is the wrong fit

• Clip longer than 60 seconds in one job
• Need 4K, HEVC-with-alpha, GIF, animated WebP, PNG sequence, or a public API / batch queue
• Need real-time virtual camera or live face tracking inside OBS
• You only need a chroma key on a perfectly even green screen and already have a local keyer—AI web removal is optional, not mandatory

ExportAlpha path

1. Sign in with Google at exportalpha.com. Most new accounts get 5 free credits.
2. Upload MP4 / MOV / WebM / M4V (limits in the spec box).
3. Download transparent VP9 WebM (default) or ProRes 4444 if the clip is ≤8 seconds and you need an editorial master.
4. Drop the WebM into OBS as Media Source.

≤60s overlay ≈ Quick $6.99 — One project ≈ Quick pack $6.99

Troubleshooting black / opaque

More cases: black background guide.

Related NLE handoff (ProRes)

If you composite in an NLE first, prefer ProRes 4444 as the handoff master, then WebM for OBS weight. ExportAlpha ProRes is ≤8 seconds; longer masters need your NLE or a local encode. See the Premiere and After Effects guides on Guides.

Frequently Asked Questions

Next step

1. Upload at exportalpha.com (Google sign-in). Most new accounts get 5 free credits.
2. Download transparent VP9 WebM (default) or ProRes 4444 MOV (≤ 8 seconds).
3. Out of trial credits? One project ≈ Quick pack $6.99 (60 credits; packs never expire).

Sources

• OBS Project, Media Sources: obsproject.com/kb/media-sources
• ExportAlpha Sources and Pricing
• Apple ProRes alpha: support.apple.com/en-us/102207 (4444 / 4444 XQ only)