Custom Field regex

Hello,

I use the following code in function.php:

<?php
add_filter('the_content', 'embedflash', 0);

function embedflash(){
    $embed = get_the_content('');

    $embed = preg_replace('#\[EMB\=(.+)]#i', '<br />blablablablablablabla)

return $embed;
?>

I put here the essential part of the code.
It allows me to use a different HTML depending on the file published on the site.
I using this code in post content:
[EMB=https://www.website.com/upload/file.xxx]

This code only works when I publish the file in the “content”, but doesn’t works with custom field. I want to insert this code into a custom field.

How can I change that please?

Thank you.