The issue is WordPress’ core configuration of TinyMCE, which strips IFRAME tags.
You can modify this configuration, to allow IFRAME tags, by hooking into tiny_mce_before_init. For example, the following code will prevent TinyMCE from stripping IFRAME, PRE, and DIV tags:
function mytheme_tinymce_config( $init ) {
// Change code cleanup/content filtering config
// Don't remove line breaks
$init['remove_linebreaks'] = false;
// Convert newline characters to BR tags
$init['convert_newlines_to_brs'] = true;
// Preserve tab/space whitespace
$init['preformatted'] = true;
// Add to list of formats to remove with Remove Format button
$init['removeformat_selector'] = 'b,strong,em,i,span,ins,del,h1,h2,h3,h4,h5,h6,pre';
// Do not remove redundant BR tags
$init['remove_redundant_brs'] = false;
// Add to list of valid HTML elements (so they don't get stripped)
// IFRAME
$valid_iframe="iframe[id|class|title|style|align|frameborder|height|longdesc|marginheight|marginwidth|name|scrolling|src|width]";
// PRE
$valid_pre="pre[id|name|class|style]";
// DIV
$valid_div = 'div[align<center?justify?left?right|class|dir<ltr?rtl|id|lang|onclick|ondblclick|onkeydown|onkeypress|onkeyup|onmousedown|onmousemove|onmouseout|onmouseover|onmouseup|style|title]';
// Concatenate
$cbnet_valid_elements = $valid_iframe . ',' . $valid_pre . ',' . $valid_div;
// Add to extended_valid_elements if it alreay exists
if ( isset( $init['extended_valid_elements'] ) ) {
$init['extended_valid_elements'] .= ',' . $cbnet_valid_elements;
} else {
$init['extended_valid_elements'] = $cbnet_valid_elements;
}
// Pass $init back to WordPress
return $init;
}
add_filter('tiny_mce_before_init', 'mytheme_tinymce_config');