The Accelerated Mobile Pages Generator automatically detects whether an iframe has been inserted on your own page and converts any iframes it finds into an <amp-iframe> tag.
Currently AMPHTML only allows content to be loaded that has a valid HTTPS connection !
The Accelerated Mobile Pages Generator automatically checks whether the URL used in the iframe can also be reached via an encrypted HTTPS connection. To do this, the Accelerated Mobile Pages Generator simply exchanges the 'HTTP' for an 'HTTPS' in the URL. If the URL can be opened with HTTPS, the Accelerated Mobile Pages generator converts the iframe into the corresponding 'amp-iframe' tag and also makes the iframe content available on the AMPHTML version.
If the URL cannot be loaded with HTTPS, the iframe content cannot be displayed directly on the AMPHTML version. In this case, the Accelerated Mobile Pages Generator displays the following placeholder graphic:
By clicking on this graphic, the user can then open the iframe content via an unencrypted 'HTTP connection'. In this way, the IFrame content can at least be accessed via an alternative solution and is not completely ignored.