Why does the site freeze when I launch an external program?

Question

PHP

Good afternoon! There is a small site (running on an nginx server) that generates video using ffmpeg and gives it to the client for download.
The code:

header('Content-type: video/mp4');

$cmd = "ffmpeg -i file.mp4..."
$process = proc_open($cmd, $descriptorspec, $pipes, getcwd());
 if (is_resource($process)) {
    while(!feof($pipes[1])){
        $chunk = fread($pipes[1], 500*1024);
        $stdout_size += strlen($chunk);
        if ($chunk !== false && !empty($chunk)){
            echo $chunk;
            if (ob_get_length()){            
                @ob_flush();
                @flush();
                @ob_end_flush();
            }
        }
    }
}

The whole thing works, but there is a minus, it lies in the fact that when 1 of the clients downloads the video, the site is unavailable (perpetual loading in the browser). As soon as the client finishes downloading the video, the site becomes available again. Tell me, please, what could be the reason? And how can this problem be solved?

Answer 1

Add workers in php-fpm pool config
You can also try updating php-fpm...