createSource (type, mimeType) {
    if (this._sourceBuffer[type] || !this.mediaSource) return
    let sb
    try {
      sb = this._sourceBuffer[type] = this.mediaSource.addSourceBuffer(mimeType)
    } catch (error) {
      throw new StreamingError(ERR.MEDIA, ERR.SUB_TYPES.MSE_ADD_SB, error)
    }
    sb.mimeType = mimeType
    sb.addEventListener('updateend', this._onSBUpdateEnd.bind(this, type))
    sb.addEventListener('error', this._onSBUpdateError.bind(this, type))
  }
@param { string } type
@param { string } mimeType