Strange error, json not working with jquery

Strange error, json not working with jquery

I am facing this strange error in using $.post.
works
$("#add-video").click(function(){
var url = $("#new-video-url").val();
$('#loader').show();
$.post( base_url + "forms/coach/get_url.php", { url:url,
base_url:base_url }, function(data){
alert(data);
$('#loader').hide();
});
});
The above piece of code, shows me the json array I am receiving using a
php file, and also shows the title field here, and hides the loader image.
But when I alert(data.title), it shows me undefined. More over, when I add
datatype 'json' to $.post,
doesn't work
$("#add-video").click(function(){
var url = $("#new-video-url").val();
$('#loader').show();
$.post( base_url + "forms/coach/get_url.php", { url:url,
base_url:base_url }, function(data){
alert(data);
$('#loader').hide();
}, "json"); //Added datatype here.
});
This neither alerts anything nor does it hide the loader image. I also tried,
$("#add-video").click(function(){
var url = $("#new-video-url").val();
$('#loader').show();
$.post( base_url + "forms/coach/get_url.php", { url:url,
base_url:base_url }, function(data){
jQuery.parseJSON(data);
alert(data.title);
$('#loader').hide();
});
});
The above one too neither alerts anything nor does it hide the loader. And
then I tried this one too that did nothing.
$("#add-video").click(function(){
var url = $("#new-video-url").val();
$('#loader').show();
$.post( base_url + "forms/coach/get_url.php", { url:url,
base_url:base_url }, function(data){
jQuery.parseJSON(data); //tried without this too.
alert(data['title']);
$('#loader').hide();
});
});
The strangest thing is that I have previously used json as I have shown in
the 2nd script(out of 4), and that works normally. My JS console too
doesn't show any errors or warning. What am I doing wrong here? How do I
access the title field of data?
If this helps, here is how I send the json array,
$json = array("title" => $title, "embed" => $embed, "desc" => $desc,
"duration" => $duration, "date" => $date);
print_r(json_encode($json));
I would really appreciate if someone can point out the error and tell me
why my scripts are failing, similar functions worked in other js file.