PrismPoster Creator Tools MCP server

creator-tools

Zero-dependency TypeScript utilities for video and social creators: aspect-ratio maths, tap tempo, subtitle parsing and conversion, platform frame sizes with sourced safe areas, encoding calculators, colour-palette extraction, GIF encoding, image metadata, and C2PA / AI-provenance detection.

No runtime dependencies. No network calls. Works in the browser, in Node, and in a worker. Every number it returns is one you could check by hand — and where a platform doesn't publish a number, it says so instead of inventing one.

npm install @prismposter/creator-tools

Why this exists

Most of these calculations are scattered across blog posts that quote each other, and a surprising number of the quoted figures are wrong. The one that started this library: every "TikTok safe area" pixel table on the open web is invented. TikTok publishes an overlay template, not a fixed inset — the occluded zone varies with frame dimensions, caption length, and which ad formats are running. There is no correct constant, so this library returns null for it and explains why, rather than shipping a plausible-looking number.

That's the rule the whole package follows:

that's what the ratio says. Every size in social-sizes is asserted against its own declared ratio by the test suite.

• Derived numbers are derived. A 9:16 frame at 1080 wide is 1920 tall because

it was read from. safeAreaSourceUrl(placement) returns that URL.

• Quoted numbers name their source. Every safe area links the first-party page

explicit kind: 'unpublished' with the reason attached.

• Unknown is a value, not a blank. A platform that publishes nothing gets an

Modules

aspect-ratio

Ratio arithmetic for frames about to be encoded. Handles non-integral cinema ratios (2.39:1) the same way it handles 16:9.

import {
  simplifyRatio, cropToRatio, padToRatio, alignToBlock,
} from '@prismposter/creator-tools/aspect-ratio';

simplifyRatio({ width: 1920, height: 1080 });   // { w: 16, h: 9 }

cropToRatio({ width: 1920, height: 1080 }, { w: 9, h: 16 });
// { result: { width: 608, height: 1080 },
//   removed: { top: 0, right: 656, bottom: 0, left: 656 },
//   areaKept: 0.3167 }

// Codecs want even dimensions; H.264 chroma subsampling makes an odd
// width an encoder error or a silent rescale.
alignToBlock({ width: 1081, height: 607 });      // { width: 1082, height: 608 }
alignToBlock({ width: 1080, height: 1920 }, 16); // { width: 1088, height: 1920 }

An odd crop remainder always goes to the bottom/right edge. That's arbitrary, but it's consistent — splitting it differently per call is how a batch of clips ends up a pixel out of register with each other.

social-sizes

Platform frames and safe areas, with sources.

import {
  getPlacement, frameSize, safeAreaPx, safeAreaBox, safeAreaSourceUrl,
} from '@prismposter/creator-tools/social-sizes';

const reels = getPlacement('instagram-reels')!;
frameSize(reels);           // { width: 1080, height: 1920 }
safeAreaPx(reels);          // { top: 269, bottom: 672, left: 65, right: 65 }
safeAreaBox(reels);         // { width: 950, height: 979 }
safeAreaSourceUrl(reels);   // Meta's Reels ads-guide page

const tiktok = getPlacement('tiktok-video')!;
safeAreaPx(tiktok);         // null — and that is the correct answer
tiktok.safeArea.reason;     // explains why no fixed table can be right

Meta publishes Reels and Stories as 14% top, 35% bottom, 6% each side. On a 1080×1920 frame that's 269 / 672 / 65 px. The bottom third is not a typo.

safeAreaPx returning null is meaningful — surface it to your user as "this platform publishes no fixed safe area". Don't substitute zeros, and don't borrow another platform's numbers.

subtitles

Shortened. The full README is on GitHub.