How to merge downloaded files with rn-fetch-blob in react native?

Question

I have the following code:

const downloadVideo = async (uri: string) => {
    var filename = `teste`;
    await RNFetchBlob
    .config({
      fileCache: true,
      path: `${RNFS.ExternalDirectoryPath}/downloads/${filename}`,
    })
    .fetch(
      "GET",
      uri,
      {"Content-Type": "octet-stream",}
    )
    .progress({ interval: 1000 },(received, total) => {
      console.log("progress", received / total);
    }).then(resp => {
      setVideoIsDownloaded(true)
    }).catch(err => {
      console.log(err)
    })
  }

I'm downloading videos that have subtitles, and I want to make them available offline in the app, but how can I download the subtitle files, as well as video information in JSON (description, title that comes from the API) and insert all of this into a single file? it's possible?

I need to download the video file, the subtitle file and insert the video information that comes from the API in a single file and retrieve them later.

I'm using the rn-fetch-blob library