Transparent background video
A video with a transparent background is an ordinary video file in which every pixel of every frame carries an alpha value, so whatever sits behind it shows through. This page is about the part that goes wrong most: transparency computed correctly, then thrown away by the format on the way out.
What “transparent” actually means in a video file
Removing a green screen and having a transparent video are two different steps. The first produces a matte — a per-pixel decision about how much of the subject is there. The second is storage: the file has to keep that matte. Most formats people reach for cannot, and when they cannot the alpha is flattened at export and the clip turns back into a rectangle. No keyer quality fixes that, because the information was discarded after the key.
Partial transparency matters here. A hard cut-out has only two values — fully there or fully gone — which is what makes keyed edges look cut with scissors. Real footage needs the in-between values along hair, motion blur and soft fabric.
Formats that carry alpha, and the one that cannot
- WebM with VP9. The open combination that genuinely stores an alpha channel and plays in Chrome, Edge, Firefox and VLC. This is what the tool writes, because it is what the browser can produce on its own.
- A PNG sequence. One transparent PNG per frame, usually zipped together. Every editor, compositor and motion-graphics tool understands it, and nothing can silently flatten it. It is also the format you want for a timeline.
- ProRes 4444 in a MOV. The professional answer, and the one that needs a desktop editor to write. Browsers cannot produce it, so it is out of scope for this site.
- GIF. Technically transparent, and technically a video, but its transparency is one bit — a pixel is either there or not — with no partial edges. Fine for a sticker, wrong for footage.
- MP4 / H.264. No alpha channel. There is no setting that turns it on. An MP4 of your subject will always be a rectangle, whatever the keyer did.
Apple’s HEVC-with-alpha is the one real exception, and it stays inside Apple’s own ecosystem — browsers give you no way to write it.
Why your transparent video plays on black
This is the most reported “my export is broken”, and it usually is not broken. A player that ignores the alpha channel has to composite the frames against something, and that something is usually black. The file still holds the transparency; the player does not.
Test it properly rather than trusting one player: drop the WebM into a page with a coloured background, or import it into an editor and put another clip underneath. If the subject floats, the alpha survived. If it floats in Chrome and sits on black in your social feed, the difference is the player, not the file.
Uploading is the hard version. Any platform that re-encodes to H.264 destroys the alpha on the way in, and nothing in the file can stop it. If the platform documents an alpha-friendly format, use that; if it does not, assume the transparency will not survive.
Making a transparent video here
- Open the tool and drop in footage shot against a green or blue backdrop. MP4 (H.264) and WebM (VP8/VP9) are the reliable inputs; MOV and OGV work when your browser can decode them, and if it cannot, the page says so.
- Let it read the key colour from the border of the frame, then adjust Tolerance, Edge and Spill while scrubbing. Blue backdrops behave the same way — see the blue screen page.
- Export a transparent WebM, a ZIP of transparent PNG frames, or the current frame as a single PNG. The video page covers what each export does under the hood.
Transparent WebM or PNG sequence?
- Pick the WebM when you need one small file that plays in a browser or in VLC. It is recorded from the keyed canvas at roughly 8 Mbps with VP9 where the browser supports it, and it takes as long as the clip does — there is no video encoder in the page, so the export runs in real time. The recorder also writes no duration into the header, so some editors show an unknown length until the file is remuxed.
- Pick the PNG sequence when the result is going into an editor or when you cannot afford a surprise. It is larger, it has no duration problem, and you choose the frame rate. Here it is capped at 1200 frames — about 100 seconds at the default 12 fps — and the page tells you to lower the rate rather than failing quietly.
- Pick the single PNG when you only need one frame.
Edges are where transparency lives
The middle of the subject is easy. The difficulty is the outline, and an outline is what a colour key can only approximate. A shadow across the screen shows why: it is the same green, only darker, so this keyer measures distance in the Cb/Cr plane and ignores brightness. Ignoring brightness is not the same as tolerating any amount of it. On our synthetic shade ramp, at the shipped tolerance of 25, the backdrop still keys out at 0.65 of full brightness (chroma distance about 29.3) and stops keying at 0.60 (about 33.5) — the alpha flips straight from 0 to 255. Raising tolerance to 50 keeps that ramp keyed down to 0.40, the darkest row in the file.
Those numbers come from generated fixtures — smooth ramps with no camera noise, no compression and no real fabric — so read them as the shape of the problem, not a promise about your footage. The full measurement is on the chroma key benchmark page, the CSV is in the reference repository, and the write-up is archived at doi.org/10.5281/zenodo.22916767.
When this does not work
- You need an MP4. There is no transparent MP4 to be had; this tool does not write one and no setting will produce one.
- Your target platform re-encodes uploads. The transparency is gone the moment it is transcoded. Use the platform’s own alpha-friendly format, or composite the clip onto a background first.
- Your player ignores alpha. The file is fine. Verify over a coloured background before concluding the export failed.
- Long clips as a PNG sequence. Capped at 1200 frames here; lower the frame rate, or take the WebM instead.
- Browsers that cannot record a canvas. Without
MediaRecorderandcaptureStreamthere is no WebM option and the PNG sequence is the fallback. - Anything that needs rotoscoping. This is a colour key. Smoke, glass, veils and flyaway hair over a moving background are beyond it, and no file format adds detail the matte never had.
- Uneven or badly lit backdrops. One global tolerance covers a lit screen or a shadowed one, not both in the same frame.
Your footage stays on your machine
Decoding, keying and recording all happen in your own browser tab: no upload, no render queue, no account, no watermark. The no-upload page explains what keeping it local avoids.