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 GIF, animated WebP, animated AVIF, and animated JPEG XL (JXL).
Pure JS, zero dependencies, works in browsers and Node.js.

Installation

npm install @jiihpeeh/is-animated

Usage

import { is_animated_blob, detect_format_blob } from 'is-animated';

const blob = await (await fetch('https://example.com/image.webp')).blob();

await is_animated_blob(blob);     // true | false
await detect_format_blob(blob);   // 'webp'

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

API

`is_animated_blob(blob: Blob, size?: number): Promise<boolean>`

Convenience wrapper — reads the first size bytes from a Blob and checks for animation. size defaults to DEFAULT_HEADER_SIZE (4096).

import { is_animated_blob, DEFAULT_HEADER_SIZE } from 'is-animated';
await is_animated_blob(blob);                 // 4096 bytes
await is_animated_blob(blob, 8192);           // custom

`detect_format_blob(blob: Blob, size?: number): Promise<'png' | 'gif' | 'webp' | 'avif' | 'jxl' | 'unknown'>`

Same as above but returns the detected image format.

`is_animated(data: Uint8Array): boolean`

Low-level — accepts a Uint8Array header. Useful if you already have the bytes.

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
JXL	Parses the codestream header to read the `have_animation` flag (raw codestream); counts `jxlp` boxes (container format)

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

Low-level — detects format from raw bytes.

Individual format checkers

Each format's animated check is also exported for direct use:

import {
  isAPNG,
  isAnimatedGIF,
  isAnimatedWebP,
  isAnimatedAVIF,
  isAnimatedJXL,
  isJXL,
} from 'is-animated';

Test

npm test

57 tests across 9 suites, including real encoded files generated by ffmpeg (lossy and lossless variants) and cjxl for JXL.

License

MIT