How to Ask Claude for an Overlay and Add It to a Video

Ask Claude to find an overlay, check its free version, and either render it as its own file or put it straight onto a local clip of up to 60 seconds. Modisign's local MCP server does the rendering on your computer, and an unchanged free preset needs no account. Changing its text or look needs Pro. You need Node 22+, FFmpeg and a desktop assistant that runs local MCP servers.

An overlay here is a short animated element, such as a location tag or a title, drawn over your footage. Alpha is the transparency channel that lets a file show only the element and nothing behind it.

What did we test, and what did we not?

We tested the published npm package @modisign/mcp 0.6.0 on macOS on October 25, 2026, signed out. Claude Desktop was not available on the test machine, so a scripted client played the assistant's part: it started the package over stdio and made the tool calls shown below. No model chose these arguments. The prompts below are what you would type; the calls are the ones a well-behaved assistant should make for them.

The footage is the first 12 seconds of a CC0 clip of a windthrow in Tammneeme, Estonia, by Sillerkiil, with synthetic speech made by the macOS say command so the file has an audio track. The overlay is the free City stop location tag.

If Modisign is not connected to your assistant yet, follow the setup in how to edit a local video with Claude first. This post starts from a working connection.

How do you get from a sentence to an overlay file?

1. Check the setup. Run npx -y @modisign/mcp doctor in a terminal. Ours reported node_ok: true, FFmpeg 7.1.1, The private render browser is ready., reachable: true and signed_in: false.
2. Ask for the free version first. For example: "Find the free location tag overlay, show me what I can change, and tell me whether my changes stay free." The assistant calls list_overlays with {"family": "location-tag", "free_only": true}. Ours returned one preset, location-tag/city-stop, with free: true and its editor link. Without free_only, the family's other presets came back with free: false.
3. Inspect the fields. get_overlay for that preset listed the 16:9, 9:16, 4:5 and 1:1 aspects, a 3.5-second duration, six looks, and each field with its limit: Place (default "Maribel old town", up to 24 characters), Detail (default "Weekend away", up to 32), colours, Layout, position and size. Each field says whether the current layout uses it.
4. Configure it. configure_overlay returns a configuration and a tier. The unchanged preset at "aspect": "16x9" came back tier: "free". When we also set an unused custom position, it stayed free and the reply said: "Kept but not used by this overlay layout: position_custom. They have no effect on this render." When we set Place to "Tammneeme, Estonia", the same call came back tier: "pro".
5. Render the standalone file. render_overlay returns a job id at once. job_status then reported queued, rendering and done, with the saved path, size and duration. Without output_dir, our file went to ~/Movies/Modisign on the Mac.
6. Or put it on your clip. "Put that tag on /Users/me/Movies/windthrow.mp4 at 4 seconds and save it as windthrow-tag.mp4." This is one add_overlay_to_video call, shown below.
7. Check the file. Scrub to the start time. If the overlay is late, early or covers something, ask for a different start and render again; your earlier file is kept.

This is the composite request we sent, with our real paths replaced:

{
  "video_path": "/Users/me/Movies/windthrow.mp4",
  "configuration": "/overlays/location-tag?aspect=9x16&look=blue-on-white",
  "start_seconds": 4,
  "output_path": "/Users/me/Movies/windthrow-tag.mp4"
}

We passed the catalog's 9:16 configuration on purpose. The reply already carried "aspect": "16x9": the tool picks the supported aspect nearest to your video and checks that version again. Paths must be full paths on your computer.

What did the files contain?

We opened every file with ffprobe and decoded frames.

Request	Saved file	What we measured
render_overlay, default format	Green-screen MP4, 135 KB	1920x1080 H.264, 30 fps, 105 frames, 3.5 s, no audio, solid green around the tag
"format": "webm"	VP9 WebM, 181 KB	Decoded with alpha: fully transparent (0) around the tag, opaque (255) on the card
"format": "mov"	ProRes 4444 MOV, 18 MB	Same alpha result, in a much larger file
add_overlay_to_video, start 4 s	H.264 MP4, 3.0 MB	1280x720 at 30 fps, 360 frames, 12.0 s, stereo AAC at 48 kHz

The composite kept the source's size and length, and its audio measured the same average loudness as the source, -20.5 dB. The tag appeared at about 4.0 seconds and was gone by 7.4 seconds, which matches a 3.5-second overlay starting at 4. The job went through queued, rendering, compositing and done in about 23 seconds on a busy test machine.

Which standalone file you need depends on your editor. Our green-screen versus transparent guide explains the trade-off. A composite avoids the question, because nothing needs keying.

Which parts are free, and which need Pro?

According to the MCP page, every free overlay renders as it is without an account, as green-screen MP4 or transparent MOV or WebM. Our signed-out test matched that, including the aspect change.

Request	Result signed out
Unchanged free preset, any format, background or aspect	Rendered
Unchanged free preset on a local video	Rendered
Free preset with your own text, look or colours	Refused: needs Pro
Any Pro preset	Needs Pro (not rendered in our test)

The refusal came before any job existed and read: "This overlay configuration needs Pro. Sign in with the login tool or run npx -y @modisign/mcp login, then retry (upgrade at https://modisign.app/pricing if the account is not Pro)." Pro costs $9 a month plus tax.

We did not approve a sign-in, so the signed-in path is untested. As documented, login gives you a link and a short code to approve in your browser, and the code expires after ten minutes. Connected computers appear on your account page, where you can disconnect one, and npx -y @modisign/mcp logout signs this computer out. Pro overlay renders also try to add a history entry to your account.

What stays on your computer?

Your video and its audio do not leave your computer. Modisign receives the overlay configuration, including any text you typed into it, to check whether the render is free. Your assistant provider sees more: your prompt, the file paths and every tool result, under its own policy, as the MCP page states.

What goes wrong, and how do you fix it?

Problem	What we saw	Fix
Overlay ends after the video	"start_seconds must be between 0 and 8.5 seconds so the overlay fits in the video."	Ask for an earlier start. The limit is video length minus overlay length
Video longer than 60 seconds	"This video exceeds 60 seconds. Use Studio for longer or multi-clip edits"	Trim it first, or use edit_video or Studio
Text too long or aspect unsupported	"Invalid MCP input" with the field and its allowed values	Shorten the text or pick a listed aspect
A change "has no effect"	The value is listed under inactive edits	Choose the layout or option that uses it
Refusal that mentions Pro	Your own text or look	Render the unchanged preset, or sign in with a Pro account
A -2 file appears	A file already had that name	Expected: our second render saved windthrow-tag-2.mp4 and left the first file alone
Render takes too long	job_status still rendering	cancel_job moved our job to canceled and left no file
"Unknown job_id"	The server process restarted	Jobs live only while the server runs. Ask again

Where should the overlay go in your video?

These are suggestions, not test results. Put a location tag in the first seconds of the shot it describes, so it reads as a caption for that place, and keep it clear of the platform's buttons using the safe-zone guide. Pick a start that leaves the whole animation inside the clip, or the tool refuses it. If you want the same element on a timeline with other clips, ask for the standalone file and place it yourself, for example with the CapCut green-screen steps.

What are the limits?

The composite takes one local video up to 60 seconds and writes an H.264 MP4 with audio, with the long side capped at 1920 pixels. We tested one 16:9 clip, one overlay family and three standalone formats on a Mac, not Windows or Linux, not a vertical video, and not an import of the WebM or MOV into another editor. Free designs are licensed for your own channels; client work and ads need Pro under the licence terms. Browse more location tag overlays or the full overlay catalog to pick a different element.