How to properly get live stream feed from another server and return the same feed with PHP

Question

I have a ZoneMinder media server that serve a live feed of CCTV's through http. It's response with an image stream (not video).

Now I making a third-party web application that needs that live stream feed to be displayed. The problem I have here, is I need to integrate the system without making any browser request to the ZoneMinder server, I wan't to do it from the third-party application backend and serve them back in the browser.

I use PHP for the application and so far I get this code running:

$link = get_zoneminder_url_stream();
header("Content-Type: multipart/x-mixed-replace;boundary=ZoneMinderFrame");
$fd = fopen($link, "r");
while(!feof($fd)) {
      echo fread($fd, 1024 * 5);
      ob_start();
      ob_end_flush();
      ob_flush();
      flush();
}
fclose ($fd);

I get the expected live image stream for the ZoneMinder server. But I get several problems.

When I start the live stream (executing the code above), the rest of my web application become unresponsive. All the request to the php script of the server can't be handled (it always 'pending' in the network tabs on the browser developer console), but still can handle other file (such as assets file) GET request.

I know that in this point, I get some problems with the PHP itself rather than the web server.

So my question is what is the best way to do a live stream request to another server from PHP server and throws back the stream as a response to the browser.

Thanks in advance