Fatal error when calling PHP-FFMpeg

Bug Report

[x] Yes, I reviewed the contribution guidelines.
[x] Yes, more specifically, I reviewed the guidelines on how to write clear bug reports.

Describe the current, buggy behavior

I am using the PHP-FFMpeg package, installed via composer. When I call the function that uses it with wp eval, the execution stops with error:

Fatal error: Uncaught TypeError: Argument 1 passed to Symfony\Component\Process\Process::__construct() must be of the type array, null given, called in phar:///usr/local/bin/wp/vendor/symfony/process/ProcessBuilder.php on line 275 and defined in wp-content/plugins/generate-hls/vendor/symfony/process/Process.php:140
Stack trace:
#0 phar:///usr/local/bin/wp/vendor/symfony/process/ProcessBuilder.php(275): Symfony\Component\Process\Process->__construct()
#1 wp-content/plugins/generate-hls/vendor/alchemy/binary-driver/src/Alchemy/BinaryDriver/ProcessBuilderFactory.php(172): Symfony\Component\Process\ProcessBuilder->getProcess()
#2 wp-content/plugins/generate-hls/vendor/alchemy/binary-driver/src/Alchemy/BinaryDriver/AbstractBinary.php(136): Alchemy\BinaryDriver\ProcessBuilderFactory->create()
#3 wp-c in wp-content/plugins/generate-hls/vendor/symfony/process/Process.php on line 140

If I launch it from web interface, it works without problems.

Describe how other contributors can replicate this bug

install PHP-FFMpeg: composer require php-ffmpeg/php-ffmpeg
create a simple function to use PHP-FFMpeg for example:

function test_ffmpeg() {
    $args = array(
      'post_type'      => 'attachment',
      'post_mime_type' => 'video',
      'posts_per_page' => -1,
      'post_status'    => 'inherit',
      'suppress_filters' => true
    );

    require_once(__DIR__ . '/vendor/autoload.php');

    $attachements = new WP_Query($args);
    foreach($attachements->posts as $attachment) {
      $source_file = get_attached_file( $attachment->ID);
        if(!file_exists($source_file)) return false;
        $ffprobe = FFMpeg\FFProbe::create();
        $metadata = $ffprobe->streams($source_file);
        var_dump($metadata->audios()->count());
    }
}

call this function via wp cli eval "test_ffmpeg();"

Describe what you would expect as the correct outcome

Get the correct information from ffmpeg.

Let us know what environment you are running this on

OS:     Linux 3.10.0-1127.10.1.el7.x86_64 #1 SMP Wed Jun 3 14:28:03 UTC 2020 x86_64Shell:  /bin/bash
PHP binary:     /usr/bin/phpPHP version:    7.4.5
php.ini used:   /etc/php.ini
WP-CLI root dir:        phar://wp-cli.phar/vendor/wp-cli/wp-cli
WP-CLI vendor dir:      phar://wp-cli.phar/vendor
WP_CLI phar path:       /home/generate/web/generate.staging.effata.it/public_html/wp-content/plugins/generate-hls
WP-CLI packages dir:
WP-CLI global config:
WP-CLI project config:
WP-CLI version: 2.4.0

wp-cli / eval-command

Fatal error when calling PHP-FFMpeg #50

Bug Report