Shared upload folder in wordpress multisite

I have a wordpress multisite, where I would like all the images uploaded through the main site (mysite.com) to be accessible to sub1.mysite.com and sub2.mysite.com. All the images should be in one folder without subdirectory (e.g: wp-content/uploads/image.jpg).
I tried the bellow function, but my images for subdomains are uploaded to wp-content/uploads/sites/#blog_id/

function wpse_16722_upload_dir( $args ) {
    $newdir = '/';

    $args['path']    = str_replace( $args['subdir'], '', $args['path'] ); //remove default subdir
    $args['url']     = str_replace( $args['subdir'], '', $args['url'] );      
    $args['subdir']  = $newdir;
    $args['path']   .= $newdir; 
    $args['url']    .= $newdir; 

    return $args;
}
add_filter( 'upload_dir', 'wpse_16722_upload_dir' );

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

This will force uploads for all sites to the wp-content/uploads directory. Sub-directories (like year/month) will still exist (if the setting is enabled).

/**
 * Force all network uploads to reside in "wp-content/uploads", and by-pass
 * "files" URL rewrite for site-specific directories.
 * 
 * @link    http://wordpress.stackexchange.com/q/147750/1685
 * 
 * @param   array   $dirs
 * @return  array
 */
function wpse_147750_upload_dir( $dirs ) {
    $dirs['baseurl'] = network_site_url( '/wp-content/uploads' );
    $dirs['basedir'] = ABSPATH . 'wp-content/uploads';
    $dirs['path'] = $dirs['basedir'] . $dirs['subdir'];
    $dirs['url'] = $dirs['baseurl'] . $dirs['subdir'];

    return $dirs;
}

add_filter( 'upload_dir', 'wpse_147750_upload_dir' );

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0