hook_form_alter doesn't load load my form_id
You have 3 options if you wish to hide a form item: 


Use .css and make your life simple using display:none;
create a custom module (see below)
Why even have the cck field if you are going to hide it? What's the point of that?


Please note that the above tutorial DISABLES the field and does not HIDE it. Disabled fields can not be edited, but they are still displayed!

To point 2:
Is this function in your themes template.php? If yes, I presume your theme is called 'video_tutorial', if not, you should rename your function so it is THEMENAME_form_alter.

However, since you're using the edit node form it will actually be using the admin theme, not your front end theme - unless you have changed permissions for certain usergroups not to be able to access the admin theme or you are using the front end theme as your admin theme (unlikely) -, so you're better off creating your own module to override the form rather than using the themes template.php file:

How to create your custom module:


Create a folder, call it whatever you like - but it should make sense - eg:

custom_admin_overrides

In it, create two blank text files:

custom_admin_overrides.info
custom_admin_overrides.module

Open custom_admin_overrides.info and add the basics so drupal can see your module:

name = Custom Admin Overrides
description = Custom Module that provides Admin Area Overrides
package = Custom
core = 7.x



Save the .info file and add the following to your custom_admin_overrides.module file:

&lt;?php
function custom_admin_overrides_form_alter(&amp;$form, $form_state, $form_id) {
 if($form_id == 'YOUR_FORM_ID') {
  $form['FIELD_NAME']['#disabled'] = TRUE;
 }
 // YOU CAN UNCOMMENT THE BELOW FOR EXTRA HELPFUL DETAILS
 // GET FORM ID UNCOMMENT BELOW
 drupal_set_message("YOUR_FORM_ID is : " . $form_id);
 // GET ALL FORM ELEMENTS UNCOMMENT BELOW
 // drupal_set_message(dprint_r($form, TRUE));
}


Note that we aren't closing the 

Save and upload the folder to your site/all/modules/custom/ folder.

Now enable the module and from that point onwards you should see the form id's displayed on all admin pages in the drupal message box at the top.

Now go to your specific node create/edit page and make a note of the form id and the field name you wish to disable. Now reopen your custom_admin_overrides.module file and replace the values for

YOUR_FORM_ID


and

FIELD_NAME


Save and now your field should be uneditable. Uncomment the following line to stop displaying the form id's:

drupal_set_message("YOUR_FORM_ID is : " . $form_id);