Make a transparent video: WebM with real alpha

Your clip is deleted the moment the cutout is sent back. Want a longer video or another output format? The full tool is on the home page.

A transparent video drops onto any background: your website, an OBS stream overlay, a slide deck, another video track. VideoBGNinja turns any clip of a person into a WebM with a genuine VP9 alpha channel: the background isn't a colour to key out, it's simply not there. Think of it as a background transparent maker for video, the same idea as a photo cutout but running on every frame instead of one, so you can make transparent background clips the way you'd make transparent PNGs. Clips can be up to 2 GB and 90 seconds on the free tier, and downloads stay background free of any watermark, with no account required.

Plenty of people want a video transparent background without learning any software first: upload the clip and the alpha channel comes back in the file. That makes this page a transparent background maker video tool in the most literal sense, and unlike a chroma key it needs no manual keying step. How to make a video transparent comes down to one upload and one download.

What people actually upload

Over the 40 days before this was written, 1,421 clips went through this exact export on our GPU. The average was 24 seconds long, and the single longest ran 23.4 minutes — someone tried anyway, even though the free limit is 90 seconds. Most people stay well inside it: 90% of uploads used less than half the allowance, with the biggest single group landing between 8 and 16 seconds (393 clips) and the next between 4 and 8 (345 clips).

The most common reason a clip gets rejected before it even starts processing is exactly that limit: in the same period, 54 uploads came back with "413 Clip is longer than 90 seconds — please trim." It's the single most frequent error on the whole site, by a wide margin. If your source footage runs long, trimming it first with any basic video app avoids the wait entirely.

There's more than one way to make background transparent video output from the same upload: download the WebM for real alpha, or the green-screen MP4 if your software needs a colour to key instead. The default WebM already has the transparent background, with no settings to touch, free for up to 10 clips a day, straight from a browser tab.

一 Where transparent WebM works

• OBS / streaming: floats over your gameplay or slides as a media source. Full setup, loop settings and a chroma-key fallback: OBS transparent overlay guide.
• Websites: <video> with WebM plays with transparency in Chrome, Edge and Firefox.
• Editors: Premiere Pro, After Effects, Final Cut and DaVinci Resolve don't import WebM alpha without a plug-in. Use the alpha matte or the green-screen MP4 there, or the ProRes 4444 MOV that comes with the paid pass (or the conversion below).
• Everything else: no alpha support? Use the included green-screen MP4 instead.

二 Pro tip: the alpha matte

Alongside the WebM you also get a black-and-white alpha matte MP4. In After Effects or Resolve, use it as a track matte on your original footage for full manual control over the composite: the same workflow studios use, without the rotoscoping.

三 When alpha isn't supported: the fallback ladder

Real alpha is the best case, and plenty of software still doesn't take it. That's not a problem as long as you know which rung to drop to, because you already have all three files. In order:

• Transparent WebM — browsers, OBS, CapCut desktop. Nothing to configure; the transparency is in the file.
• Alpha matte — the rung to take the moment the WebM misbehaves in your editor. It's a black-and-white video: white is the subject, black is background. Put your plain footage on one track and the matte on another, then set the matte as a luma key or track matte. Every editor of the last twenty years can do this, and it gives you more control than alpha does — you can blur the matte slightly for a softer edge, or choke it inward by a pixel to kill a rim.
• Green-screen MP4 — for anything that only knows chroma key. PowerPoint and Keynote both fall here: neither honours video alpha, but PowerPoint has "Set Transparent Color" for video and Keynote has Instant Alpha, and both key a flat green happily. Same for hardware switchers, older editors and most phone apps.

Rule of thumb: alpha where it's supported, matte where it isn't, green where nothing else fits.

One platform note that saves an afternoon: transparency is a property of the file, not of the internet. Upload a transparent WebM to YouTube, Instagram or TikTok and it comes out flattened, because their players composite everything onto opaque video. Alpha is for things you control — your own page, your own stream, your own edit.

四Converting to what your tool wants

If your editor insists on a particular intermediate, ffmpeg does it locally in seconds. It's free, it runs everywhere, and nothing leaves your machine — which matters if the footage is a client's.

WebM to ProRes 4444, real alpha, the safest thing to hand a professional editor:

ffmpeg -c:v libvpx-vp9 -i alpha.webm -c:v prores_ks -profile:v 4444 \
       -pix_fmt yuva444p10le -alpha_bits 8 out.mov

WebM to a PNG sequence, for After Effects or an animated sticker:

ffmpeg -c:v libvpx-vp9 -i alpha.webm frames/%04d.png

Bake it onto a solid colour — white, or your brand colour — as a normal MP4:

ffmpeg -f lavfi -i color=white:s=1280x720 -c:v libvpx-vp9 -i alpha.webm \
       -filter_complex "[0:v][1:v]overlay=shortest=1" \
       -c:v libx264 -crf 18 -pix_fmt yuv420p out.mp4

And the check that catches the one silent failure: ffprobe -v error -select_streams v:0 -show_entries stream_tags=alpha_mode -of csv=p=0 file.webm should print 1. If it prints nothing, the alpha is gone, almost always because something re-encoded the file to H.264 along the way, which flattens transparency to black without a warning. Don't go by the pixel format: ffprobe reports yuv420p even for a VP9 file with alpha, because the alpha is stored as a separate layer, and that is also why every ffmpeg command above starts with -c:v libvpx-vp9 before the input. Without it ffmpeg's built-in decoder drops the alpha. Keep the WebM you downloaded as the master and treat every conversion as a copy. That one ffprobe line is a transparent video checker, and the commands above convert the transparent video to whichever format your tool wants. The alpha needs VP9 in a WebM; a plain transparent video mp4 can't hold it, which is why the green-screen MP4 export exists as a fallback.

Searching to make mp4 transparent usually leads here by mistake: MP4 has no alpha channel, so a transparent mp4 file the way people picture it doesn't exist; the WebM carries the transparency and the green-screen MP4 is the fallback to key out. If you were wondering how to make a PNG sequence with transparency instead, the ffmpeg command above turns the WebM into one. Between the WebM, the ProRes 4444 command and the PNG sequence, this page covers the transparent formats most tools ask for, and the cut-out itself works as a transparent video converter free of charge.

五 Making the composite look real

A perfect cut-out can still look pasted on, and it's almost never the edge that gives it away. Five things do, in roughly this order of how much they matter:

• Light direction. If your face is lit from the left and the new background is lit from the right, viewers read it as wrong immediately without being able to say why. Pick a background whose light comes from your side, or flip the background horizontally — it's usually the cheapest fix in the whole edit.
• Brightness and contrast. Footage shot in a dim room dropped onto a bright outdoor scene stays visibly dimmer. Grade the subject and the background together as one image at the end, not separately.
• A contact point. A person standing on nothing floats. If your subject's feet or the base of a product are in frame, add a soft blurred dark oval underneath at low opacity. It's ten seconds of work and it does more for believability than any edge setting.
• Scale and eye level. A subject filmed at chest height composited into a background shot from the floor gives two horizons in one frame. Match the eye line roughly and nobody looks twice.
• The frame edge. If you were cropped at the bottom of your original clip, the cut-out ends in a dead straight line there. Composited over open space that reads as a cardboard cut-out. Either keep that edge at the bottom of the new frame too, or crop the composite so the straight edge stays out of view.

One edge trick worth knowing, for when the outline looks a touch too crisp against a soft background: feather the alpha by a single pixel. In an editor that's a small blur applied to the matte, not to the footage. Real camera edges have a hint of softness because lenses do; a mathematically perfect edge is the one thing a real shot never has.

六Questions

Also here: turn a video into a GIF, trimmed to the seconds you pick, or with the person cut out so the background stays see-through in the loop. The cut-out GIF runs on the same engine as this page and covers the first 10 seconds of the clip: pick "Cut out the person" on the home page and every upload comes with one.
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By Sam Ridder — I build and run VideoBGNinja on my own hardware, on my own. Who I am.

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