WordPress default audio playlist – how to add custom caption?

If I’m not mistaken, then you can’t do that with the playlist shortcode by default.

How often does this case happen? If it rarely happens, it might be easiest to upload the file a second time, and change the caption, information as needed.

Create your own playlist shortcode code based on the default one found in wp-includes/media.php. As for the approach, for example, if custom shortcode attribute is present, then replace caption (title or whatever), secondary information can be saved in custom fields, else keep the default. You can deregister the default shortcode and then register your custom code to .