Render audio context

render_audio_context.js

/**
 * Renders an offline audio context into an audio buffer.
 * Considers timeout and suspension.
 *
 * The `context` argument is an instance of OfflineAudioContext.
 */
function renderAudio(context) {
  return new Promise((resolve, reject) => {
    context.oncomplete = (event) => resolve(event.renderedBuffer)

    // 3 tries to start the context when the page is in foreground
    let resumeTriesLeft = 3

    const tryResume = () => {
      context.startRendering()

      switch (context.state) {
        case 'running':
          // The context has started calculating the audio signal. Start a plain timeout.
          setTimeout(() => reject(new Error('Timeout')), 1000)
          break
        case 'suspended':
          // Don’t count the tries when the page is in background
          if (!document.hidden) {
            resumeTriesLeft--
          }
          if (resumeTriesLeft > 0) {
            setTimeout(tryResume, 500) // There is a delay before a retry
          } else {
            reject(new Error('Suspended'))
          }
          break
      }
    }

    tryResume()
  })
}