What free tools can export a transparent WebM with alpha?
It depends on whether your clip already has transparency. If it does (a ProRes 4444 MOV, for example), free encoders such as FFmpeg can write VP9 WebM with alpha. If it does not, you need background removal first: a browser AI remover, a green-screen key, or rotoscoping. Free AI tiers differ in clip length, resolution, sign-up, and watermark, so check the export is WebM with alpha, not an MP4 with a filled background.
Updated
Five free credits, then a real alpha file
Most new accounts get 5 credits, which is up to 5 seconds of video. The default download is transparent WebM.
5 free credits on first sign-in for most new accounts. Trial stills capped at 5. No card required. Fair-use limits apply.
Two different jobs
Encoding a file that already has alpha is not the same job as removing a background. A free encoder does not invent a matte. A free AI tier that only hands you an MP4 did not give you a transparent WebM. Split the question before you compare tools.
Already has alpha: encode WebM
| Route | Type | Runs where | Writes VP9 alpha WebM | Notes (source, checked 2026-10-09) |
|---|---|---|---|---|
| FFmpeg | CLI | Local | Yes. libvpx-vp9, pixel format yuva420p while encoding. | Tested here on FFmpeg 6.1.1 with libvpx 1.14.0. See ProRes MOV to WebM if the source is already ProRes, and MP4 to transparent WebM for a flat-color key. |
| Desktop editors | Local app | Local | Only if that editor's own export includes alpha. Confirm in the editor's manual. | This page does not claim a specific editor version writes VP9 alpha. Export an alpha intermediate, then encode with FFmpeg if you need WebM. |
| Browser-based WebM encoders | Web page | In the browser | Depends on the page. Confirm the downloaded file. | Useful when you cannot install FFmpeg. Limits change. Check the tool's own page. |
| ExportAlpha | Web app | Cloud | Yes. Transparent WebM is the default export. | Also removes the background. 5 free credits on first sign-in for most new accounts. WebM up to 60 seconds. ProRes 4444 up to 8 seconds. No HEVC-with-alpha. |
Limits change; check each tool's page.
Ordinary video: remove the background first
| Route | Method | Sign-up | Free limits | Alpha export | Where it runs |
|---|---|---|---|---|---|
| AI web removers | AI | Varies | Varies. Read the length, sign-up, and watermark rules on that tool's own page. | Must be WebM or ProRes with alpha, not a filled MP4. | Often cloud |
| Browser-local removers | AI or a single color, on the device | Often none | Check the tool. This page does not copy another site's cap. | Check the file. | Local in the browser |
| Green-screen keyers | Chroma key, not AI | Often none | Your own computer | WebM, or an editor format that stores alpha | Local |
| ExportAlpha | AI | Google sign-in | 5 free credits on first sign-in for most new accounts (up to 5 seconds of video). Fair-use limits apply. | WebM VP9 up to 60 seconds. ProRes 4444 up to 8 seconds. No watermark on the video. No HEVC-with-alpha. | Cloud |
Limits change; check each tool's page.
How to check a file really has alpha
On FFmpeg 6.1.1, a default ffprobe of a VP9 WebM with alpha reported pix_fmt=yuv420p and the tag alpha_mode=1. Decoding the same file with -c:v libvpx-vp9 reported yuva420p, and the transparent pixels had alpha 0. The default vp9 decoder treated those pixels as opaque.
ffprobe -v error -select_streams v:0 -show_entries stream=pix_fmt:stream_tags=alpha_mode -of default output.webm
ffmpeg -hide_banner -c:v libvpx-vp9 -i output.webm -f null -Also play the WebM in Chrome over a colored page. If the page color shows through, alpha is compositing. A system player that paints black is not a failed file. Safari is a separate case: WebKit bug 275908 describes a grey background, not a successful composite.
Still images are a different free-credit question. See what free means for the still-image remover. Video and stills share one credit pool.
Frequently Asked Questions
Is there a completely free way to make a transparent WebM?
Yes, if the clip already has an alpha channel. FFmpeg can encode that file to VP9 WebM with alpha on your own computer, at no charge from ExportAlpha. If the clip is an ordinary video with a real background, something has to create the matte first. ExportAlpha's free tier is 5 credits on first sign-in for most new accounts, which is up to 5 seconds of video.
Can I convert an MP4 to a transparent WebM for free?
Only if you create the alpha yourself. An everyday MP4 has no alpha channel. A flat green, blue, black, or white background can be keyed with FFmpeg. A real scene needs background removal. The guide How do I convert an MP4 with a solid background into a transparent WebM? has the tested commands.
Why does my free tool export MP4 instead of WebM?
Many removers fill a new background and write an H.264 MP4. That file can look clean in a player and still have no alpha channel. Ask for WebM with alpha, or ProRes 4444, and check the file before you publish it.
Do free AI background removers add a watermark?
ExportAlpha does not watermark video exports. Trial and paid video jobs use the same video path. Other tools set their own rules. Check the file you downloaded.
Does transparent WebM work in Safari?
Safari plays WebM, but WebKit bug 275908 describes a grey background rather than transparency. Chrome, Firefox, and Edge can composite VP9 alpha. The guide How do I make one transparent video work in both Safari and Chrome? covers delivery. ExportAlpha does not export HEVC-with-alpha.
Which is better for OBS, WebM or MOV?
VP9 WebM with alpha is the usual OBS overlay: smaller, and OBS Media Source lists .webm. ProRes 4444 MOV also works and is much larger. ExportAlpha limits ProRes to 8 seconds. Do not add a chroma key if the file already has alpha.
How many seconds can I process free on ExportAlpha?
Most new accounts get 5 free credits on first sign-in. 1 credit = 1 video second, rounded to the nearest whole second, so that is up to 5 seconds of video. No card is required. Fair-use limits apply. WebM exports can run up to 60 seconds once you have the credits. ProRes 4444 is limited to 8 seconds.
Sources
- FFmpeg 6.1.1 / libvpx 1.14.0, chromakey and colorkey to VP9 alpha, tested October 9, 2026 on a synthetic clip. Filter descriptions: ffmpeg-filters (retrieved October 9, 2026).
- OBS Media Source file types, including .webm and .mov: OBS Knowledge Base (retrieved October 9, 2026).
- WebKit bug 275908: grey background rather than transparent (status NEW, retrieved October 9, 2026).
- ExportAlpha limits: Sources
Try a short clip
Five free credits on first sign-in for most new accounts. The download is transparent WebM, not a filled MP4.
5 free credits on first sign-in for most new accounts. Trial stills capped at 5. No card required. Fair-use limits apply.