Best way to configure HTTP header content-length

Hello,

I have a video player that makes a request via Servlet that already works and I need to include a new video.

At first I will return the video according to the logged in user.

The problem I came across is that the videos are of different sizes and the response header has a pre-defined content-Length setting that I believe is from the video that already exists:

response.setHeader("Content-Length", "15800000");

I researched about the header properties and I did not understand if it is valid to omit this value or try to somehow schedule the change of this response header.

This is the Servlet:

    public void doGet(HttpServletRequest request,HttpServletResponse response) throws IOException {
    try (FileInputStream fin = new FileInputStream(FileServerUtil.getFileServer()
            + PASTA_MEDIA + File.separator + NOME_ARQUIVO);
         ServletOutputStream out = response.getOutputStream()) {
        response.setContentType("video/mp4");
        response.setHeader("Access-Control-Allow-Origin", "*");
        response.setHeader("accept-ranges", "bytes");
        response.setHeader("cache-control", "public,max-age=14400,public");
        response.setHeader("Content-Length", "15800000");

        byte [] buf = new byte[4096];
        int read;
        while((read = fin.read(buf)) != -1) {
            out.write(buf, 0, read);
        }
    } catch (Exception e) {
        logger.error(e);
    }
}

I could put an if else and change the header according to the video but I believe it would be a "dumb" way to do it. I would like a suggestion on this!