Possible to hook into Media Library preview File column and use a custom image?

Question

The project I'm working on, I couldn't find an easy way to have WordPress create the thumbnails sizes I needed without tons of waste, nor to simultaneously generate WebP versions, so I disabled the thumbnails, I upload a full-size jpg or png, and then I manually generate my WebP and other sizes and copy them to the uploads. A custom PHP function handles building responsive <picture>.

However, I'd like to avoid the media library loading up the full-size image as the thumbnail all the time, as it's a waste of bandwidth. I'd like to point to a small WebP or JPG version that is not in the library but in the uploads folder and have it load that image instead. The file name is almost the same, just needs to be appended with _width (width being a number) which I could do with strtr or something.

Is there a way to access the Media Library File column with a function and a hook/filter so I can change the src path to the thumbnail image? I'd also need to avoid PDF, SVG and TXT file uploads and just target JPG or PNG files. If it's not possible, I'll have to generate a thumbnail with a custom size.

Answer 1

I managed to solve this after being pointed in the right direction. In my case, I filtered wp_get_attachment_image_attributes to change all the paths in the admin for attachments at once.

In my case, I am using descriptive suffixes on all my image files (i.e. _featured etc) so modifying them was easy using strtr which I also used to change the extension from jpg to webp.

Now all attachment image previews load in the files I want in the correct format at the desired size, and it works for Media Library, featured images, and custom fields.

add_filter( 'wp_get_attachment_image_attributes', 'my_attachment_filter', 10, 3 );
function my_attachment_filter($attr, $attachment, $size){
    if (is_admin()){
        if (array_key_exists( 'src' , $attr)){
            $old_src = $attr['src'];
            $new_src = strtr($old_src, array('_featured' => '_featured_eighth', '_portrait' => '_portrait_204', '_og.' => '_og_320.', '.jpg' => '.webp'));
            $attr['src'] = $new_src;
        }
    }
    return $attr;
}