How to replace custom post type slug with an ACF value?

Can be the $cptslug value dynamic according to ACF value?

Yes, it can.

Here’s how:

1. First off, my ACF field settings are as follows:

   Name: video_or_image
   Type: Select
   Options:

   1 : Video
   0 : Image
   

2. So I register the post type like so, where the rewrite slug is set to %video_or_image% — i.e. %{Name of the ACF field}%, but you don’t have to follow that format:

   register_post_type( 'video', array(
       'label'   => 'Video',
       'public'  => true,
       'rewrite' => array(
           'slug' => '%video_or_image%',
       ),
       ...
   ) );
   

   Or if you want to or can only use the register_post_type_args to change the rewrite slug, then just set the $cptslug to %video_or_image%.

3. Next, I register the rewrite tag (%video_or_image%) after the register_post_type() call, which is hooked to the init action:

   add_rewrite_tag( '%video_or_image%', '([^/]+)' );
   

   Registering the tag is mandatory, and ensures that the tag is properly replaced with the RegEx pattern (i.e. ([^/]+)) when the rewrite rules are saved:

4. Then I replace the rewrite tag with the proper (ACF) field value using the post_type_link filter:

   add_filter( 'post_type_link', function( $url, $post ){
       if ( 'video' === $post->post_type ) {
           $value = get_field( 'video_or_image', $post->ID );
           $url = str_replace( '%video_or_image%', $value, $url );
       }
   
       return $url;
   }, 10, 2 );
   

That’s all, but don’t forget to flush the rewrite rules — simply visit the permalink settings page.

And I suggest you to set a default value for your ACF field, and use “better” values if possible.. I mean, other than 1 or 0.. but if you’re sure about such values, then (I think) it’s alright. =)

UPDATE

In my case, using only ([^/]+) in the rewrite tag, causes troubles when loading Pages (i.e. page post type):

add_rewrite_tag( '%video_or_image%', '([^/]+)' );

How I solved the problem

1. Use a unique identifier, e.g. v/ as in:

   add_rewrite_tag( '%video_or_image%', 'v/([^/]+)' );
   

   Then in the post permalink, v/ should also be added to the rewrite tag replacement value — see step #4 above:

   $url = str_replace( '%video_or_image%', 'v/' . $value, $url );
   

2. I restricted the ACF field value to numeric, then I used:

   add_rewrite_tag( '%video_or_image%', '(\d+)' );
   

   That (\d+) does not guarantee no conflict with other rewrite rules, but at least in my case, it worked.

Sorry about the ([^/]+) — I thought the 0 and 1 values were just examples. I should’ve just used (\d+).