Feature types

• decoders - decode images.
• encoders - encode images.
• processors - change images, generally in a way that potentially aids compression.
• preprocessors - prepares the image for handling.

The key difference between preprocessors and processors is each 'side' in Squoosh can process differently, whereas a preprocessor happens to both sides.

Adding code to the worker

Any feature can have a worker folder. Any script in that folder will have its default export bundled into the worker, using the name of the file.

So, processors/shout/worker/shout.ts:

export default function () {
  console.log('OI YOU');
}

…will be bundled into the worker and exposed via comlink as shout().

Folders

Within a feature, files in the:

• client folder will be part of the client project.
• worker folder will be part of the worker project.
• shared folder will be part of the shared project. Both the client and worker projects can access the shared project.

Encoder format

Encoders must have the following:

shared/meta.ts which exposes the following:

• label - The name of the codec as displayed to the user.
• mimeType - The mime type to be used when generating the output file.
• extension - The file extension to be used when generating the output file.
• EncodeOptions - An interface for the codec's options.
• defaultOptions - An object of type EncodeOptions.

client/index.ts which exposes the following:

• encode - A method which takes args:
  • AbortSignal
  • WorkerBridge
  • ImageData
  • EncodeOptions

And returns (a promise for) an ArrayBuffer.

Optionally it may export a method featureTest, which returns a boolean indicating support for this decoder.

Optionally it may export a component, Options, with the following props:

interface Props {
  options: EncodeOptions;
  onChange(newOptions: EncodeOptions): void;
}

…where EncodeOptions are the options for that encoder.