Rotoscope Mask Editor
Draw an outline around a subject in the source video and adjust it at manual keyframes. Corresponding vertices move linearly on sampled frames in between. You can keep one transparent hole inside the contour. The output is a real white/transparent RGBA PNG sequence plus normalized coordinates in JSON. There is no automatic subject detection: inspect intermediate frames and add keyframes when motion needs them.
Key features
- Edit first and last frames plus up to 12 manual contour keyframes
- Keep 3–16 outer vertices and an optional inner hole consistent across all keyframes
- Interpolate matching vertices at sampled frames and reject crossing or out-of-bounds geometry
- Export real alpha PNG frames in a ZIP plus a separate frame-path JSON
- Edit by dragging or accessible X/Y fields and record the local source SHA-256 in the output
How to use
- Choose a browser-decodable MP4/WebM of at most 6 seconds and 64 MiB, or create the moving video example.
- Move the outer vertices at the first and last sampled frames, or enter X/Y percentages, then save each keyframe.
- Optionally add a hole and save more keyframes where motion changes. Scrub the interpolated frames to inspect them.
- Render the mask sequence, download the PNG ZIP and path JSON, and inspect the alpha in your editor.
Use cases
- Create a hand-drawn alpha mask for compositing a moving subject
- Adjust an outline as its shape changes across a short clip
- Leave a transparent opening inside a subject contour
- Keep frame coordinates as JSON for another local editing workflow
Frequently asked questions
Does it automatically track a person or object?
No. You place the outline and adjust each keyframe. Corresponding vertex numbers move linearly between them; complex motion needs more manual keyframes.
Are the PNGs truly transparent?
Yes. For each sampled frame the outer polygon becomes opaque white, while the outside and optional inner hole have alpha zero. The ZIP includes paths.json and the same path JSON is available separately.
Does it encode a transparent video?
No. This tool exports a sequence of PNG alpha masks, not a video. It does not include source color, audio, subtitles, or metadata.
How are contours and holes interpolated?
Corresponding vertex indices move linearly across first, last, and any middle keyframes. Every keyframe must have the same outer vertex count and the same hole topology. Crossings or holes leaving the contour are rejected before export.
Does it process every original frame?
No. It samples up to 6 seconds at 8 frames per second, at most 48 analysis frames. The masks do not use the source frame rate or full resolution, so fast motion can be missed.
What files and privacy limits apply?
Browser-decodable MP4/WebM/MOV up to 64 MiB is supported, and the output ZIP is limited to 32 MiB. The source stays in browser memory and is not sent to this tool's server.
Privacy
Source video and decoded frames stay in this browser's memory. The tool does not upload them to its server. Clear the editor or close the tab to release media URLs.
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