[Plugin: Custom Content Type Manager] Automatic insert custom field content into YouTube embed code

How can I edit my code so that my custom field is the ID code of a YouTube video (e.g. s6jaYJx7yeI) and it is automatically output as an embedded video.

That is, the custom field is automatically inserted into here:

<iframe width="420" height="315" src="https://www.youtube.com/embed/CUSTOMFIELDVALUEHERE" frameborder="0" allowfullscreen></iframe>

All of the different things I’ve tried with custom field either kill the iframe callout or block off the code at /embed. I can’t seem to get it neatly inserted into the source callout. Help!

https://www.ads-software.com/extend/plugins/custom-content-type-manager/