How do I find a Form_ID for hook_form_FORM_ID_alter?
The form ID is used as the id attribute on the form when it renders.

For content types the pattern is also predictable:  node-[TYPE_NAME]-form.  So in your case you're looking for:  hook_form_node_videos_form_alter().

Another way to handle it is to use the main hook_form_alter() and check the $form_id parameter when you load the form you'd like to target.