svga-web/src/parser/worker.ts

A SVGA player for modern Web.

import { inflate } from 'pako'
import VideoEntity, { AudioSources, ImageSources } from './video-entity'
import { com } from '../proto/svga'
import svga = com.opensource.svga

enum BinaryPrefix {
  /**
   * audio/x-mpeg
   * SUQz in base64
   * 0b01001001, 0b01000100, 0b00110011
   */
  AUDIO_XMPEG = 0b01001001,
  /**
   * image/png
   * iVBO in base64
   * 0b10001001, 0b01010000, 0b01001110
   */
  IMAGE_PNG = 0b10001001,
}

onmessage = function (event: MessageEvent<{ data: ArrayBuffer; id: number }>) {
  const inflateData: Uint8Array = inflate(new Uint8Array(event.data.data))
  const movie = svga.MovieEntity.decode(inflateData)
  const images: ImageSources = {}
  const audios: AudioSources = {}
  const transferables = new Set<Transferable>()

  // parse audios
  movie.audios.forEach((audio) => {
    const { audioKey, endFrame, startFrame, startTime, totalTime } =
      audio as svga.AudioEntity
    const uint8 = movie.images[audioKey]
    if (!uint8) {
      return
    }

    const sourceBuffer = uint8.buffer.slice(
      uint8.byteOffset,
      uint8.byteOffset + uint8.byteLength,
    )
    transferables.add(sourceBuffer)
    audios[audioKey] = {
      audioKey,
      source: sourceBuffer,
      startFrame,
      endFrame,
      startTime,
      totalTime,
    }
  })

  // parse images
  for (const key in movie.images) {
    const uint8 = movie.images[key]

    // skip audio data, no work needed here
    if (uint8[0] === BinaryPrefix.AUDIO_XMPEG) {
      continue
    }

    // only support png now
    if (uint8[0] !== BinaryPrefix.IMAGE_PNG) {
      console.warn('unrecognized svga image source', uint8, movie)
      continue
    }

    const sourceBuffer = uint8.buffer.slice(
      uint8.byteOffset,
      uint8.byteOffset + uint8.byteLength,
    )
    images[key] = sourceBuffer
    transferables.add(sourceBuffer)
  }

  const data = new VideoEntity(movie, images, audios)

  const transfers = Array.from(transferables)
  postMessage({ result: data, id: event.data.id }, transfers)
}