You can do this to heck the URL value. There are few different ways for the user to enter a URL so they all need to be covered
acf.addAction('load_field/key={the key of your oembed field}', function(field) {
$(field.$el).on("change", "input[type=text]", function(e){
let val = $(this).val();
// pass val to your validation method
});
$(field.$el).on("click", "input[type=text]", function(e){
let val = $(this).val();
// pass val to your validation method
})
$(field.$el).on("keyup", "input[type=text]", function(e){
let val = $(this).val();
// pass val to your validation method
})
})
