gif-wasm-codec v0.1.0

gif-wasm-codec

A WebAssembly library to encode and decode gifs in the browser.

This project is essentially a wrapper over the gif crate written in Rust,

Notes

This project is incomplete - many options exposed by the underlying crate are not configurable. However, the default options should be sufficient for most use cases (like in my image splitter).

Decoding works well and is faster than most JS-only libraries that I've tested. Encoding, on the other hand, has not been fully optimized/may have memory issues and until WASM is more mature I don't see it being faster than a pure JS + web workers approach.

Usage

Install the library from npm.

yarn add gif-wasm-codec

Import the library.

import * as gif from 'gif-wasm-codec'

API

Using this library at the moment requires a bit of manual work; my focus has been on correctness and optimization, so I haven't built out any abstractions yet.

decode(arr: Uint8Array) -> DecodedGif takes a Uint8Array representing an image and returns a DecodedGif object.

DecodedGif is the interface representing the outcome of a call to decode. Contains three items:

• num_frames is the number of frames in the gif.
• metadata is a flattened array of five-tuples in the form of (delay, top, left, width, height). The slice metadata[5i..5i+5] represents these values for the ith frame.
• frames is a flattened array of the image data for all frames. Note that with some compression techniques, not every frame will be the same size. We use the metadata to compute the size: width * height * 4 (RGBA).

Example: View all frames of an uploaded gif.

const fileInput = ... // Some input with type file
fileInput.addEventListener("input", async function () {
  const file = decodeInput.files![0];
  const buf = await file.arrayBuffer();
  const results = gif.decode(new Uint8Array(buf))

  let frameIdx = 0
  for (let i = 0; i < num_frames; i++) {
    const [
      delay,
      top,
      left,
      width,
      height
    ] = metadata.subarray(
      i * 5,
      (i + 1) * 5
    );

    const size = width * height * 4;
    const frame = frames.subarray(i, i + size);
    frame_idx += size;

    const imgData = new ImageData(frame, width, height);
    const canvas = document.createElement("canvas");
    const ctx = canvas.getContext("2d")!;
    canvas.width = width;
    canvas.height = height;
    ctx.putImageData(imgData, 0, 0);
    document.body.append(canvas);
  }

  results.free()
})

Encoder is not recommended for use. Use something like gif.js instead.