Package Exports

@jiihpeeh/is-animated
@jiihpeeh/is-animated/index.js

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Readme

is-animated

Detect whether an image is animated by inspecting its binary header.

Supports APNG (animated PNG), animated GIF, animated WebP, and animated AVIF.
Pure JS, zero dependencies, works in browsers and Node.js.

Install

npm install is-animated

Usage

import { is_animated, detect_format } from 'is-animated';

const response = await fetch('https://example.com/image.webp');
const blob = await response.blob();
const bytes = new Uint8Array(await blob.slice(0, 4096).arrayBuffer());

is_animated(bytes);   // true | false
detect_format(bytes); // 'png' | 'gif' | 'webp' | 'avif' | 'unknown'

Only the first few KB are needed — the animation markers live in the file header.

API

`is_animated(data: Uint8Array): boolean`

Returns true if the image has multiple frames (is animated).

Format	Detection method
APNG	Scans for the `acTL` chunk after the PNG signature
GIF	Counts image descriptors (`0x2C`) in the block structure
WebP	Checks the VP8X chunk animation flag (bit 1) or looks for an `ANIM` chunk
AVIF	Looks for `moov` or `moof` boxes in the ISOBMFF container

`detect_format(data: Uint8Array): 'png' | 'gif' | 'webp' | 'avif' | 'unknown'`

Returns the detected image format. Fast path — only reads the file signature.

Test

npm test

46 tests across 8 suites, including real encoded files generated by ffmpeg (lossy and lossless variants).

License

MIT