<svg viewBox="0 0 200 100" width="200px">
  <defs>
    <mask id="mask">
        <path d="M20,50 180,50 M160,30 180,50 160,70" fill="none" stroke="#fff" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
    </mask>
  </defs>
  <rect fill="#000" width="100%" height="100%" mask="url(#mask)">
    <animate attributeName="width"
             dur="2s"
             begin="0s"
             values="0%; 80%; 50%; 100%"
             fill="freeze"/>
  </rect>

</svg>