Media category plugin building

Hey,

I’m currently working on a plugin that adds a category field to any media items.

I’m currently using hooks to achieve that, but there’s some little issues that I can’t resolve.

https://pastebin.com/f38f800db

Here is my code, I simply add a select list to the edit media page which is working fine. My problem here is that it doesn’t send the value in ‘the attachment_fields_to_save’ proccess, how can I achieve that? I searched for other hooks function and found nothing related to this.

So I hope someone knows a way to do it, thanks.