The question is related to DRUPAL modules name is 'Video Embed Field' module.
The default output of this module generated the Youtube iframe embed as set in the config by Administrator. But... The iframe's attribute can be set only for width, height, src but no 'id'. What I want is to hard-code into the module core and add 'id' attribute into the iframe, so every time I setup the embed field I have an id on the iframe.
I cannot find the place where the module core generate the iframe attribute...