Question

This is more an operating systems question than a PHP question, but here it is regardless:

I’m looking to run ffmpeg via shell_exec() to convert uploaded videos to different formats. I’m wondering how the OS handles multiple ffmpeg commands when multiple videos are uploaded.

Here is some example code to make it more explicit:

<?php

  $filePath = upload($_FILE['video']); //get filepath from uploaded file

  shell_exec('ffmpeg ' . $filePath . ' video.mp4'); //simple ffmpeg conversion

?>

Assume the OS is linux-based.

• Will the OS create a thread for each command until it runs out of memory using the code above?
• I’m assuming that creating some sort of queue is a better way of handling these calls, but does that mean the system will only be converting one video at a time?
• What if I wanted the system to be converting multiple videos in parallel, and what is a good way of knowing the max number of parallel threads a system can handle before it becomes overburdened?

Thanks.

Answer 1

PHP will fork off a separate process for every individual shell_exec command that is executed.

Queuing these jobs up would be a good idea. So would running them in the background, rather than delaying the response from PHP until both the upload and the ffmpeg job are done. PHP does not have any built-in way to do this, but there are a number of libraries, like Gearman, for managing tasks like this.

For CPU-bound jobs like video conversion, a good rule of thumb is one process per physical CPU core.