a.js

{
  availabilityStartTime: Date,
  baseURL: string,
  duration: number,
  id: string,
  locations: [string],
  suggestedPresentationDelay: number,
  timeShiftBufferDepth: number,
  transportType: "dash",
  type: string,
  periods: [{
    baseURL: string,
    duration: number,
    id: string,
    start: number,
    adaptations: [{
      accessibility: [string],
      baseURL: string,
      id: string,
      lang: string,
      type: string,
      representations: [{
        bitrate: number,
        baseURL: string,
        codecs: string,
        height: number (pixels),
        id: string,
        index: {
          // TODO
        },
        mimeType: string,
        width: number (pixels),
      }]
    }]
  }]
}