watch.html

<style>
  body {
    margin: 0px;
    background-color: black;
  }
</style>

<video
  style="width: 100vw; height: 100vh"
  id="video"
  controls
  preload="metadata"
></video>

<script>
  let searchParamsString = window.location.search.substring(
    1,
    window.location.search.length
  );

  let searchParams = {};

  let searchParamsArray = searchParamsString.split("&");
  console.log({ searchParamsArray });

  searchParamsArray.forEach((fullParam) => {
    let [paramName, paramValue] = fullParam.split("=");
    searchParams[paramName] = paramValue;
  });

  console.log({ searchParams });

  let videoElement = document.querySelector("video#video");

  videoElement.innerHTML = `
     <source src="/video/${searchParams.filmPath}" type="video/mp4" />
     <track label="English" kind="subtitles" srclang="en" src="/sub/${searchParams.subPath}" default />
  `;
</script>