I hope, this works:

Add BlogEntry::allow_wysiwyg_editing(); to /mysite/_config.php

And comment out this two lines in the BlogEntry.php:
$fields->removeFieldFromTab("Root.Content.Main","Content");
$fields->addFieldToTab("Root.Content.Main", new TextareaField("Content", _t("BlogEntry.CN", "Content"), 20));

Hi there,

you can add any type of fields to DataObjects.

Here is an example of a DataObject to embed videos from youtube

<?php

class Videos extends DataObject {
	
	static $db = array(
		'Title' => 'Varchar(255)',
		'Description' => 'Text',
		'YouTubeCode' => 'HTMLText' //code to embed the video
	);
	
	function getCMSFields() {
	  	$fields = parent::getCMSFields();

	  	$fields->addFieldToTab('Root.Main', new TextField('Title', 'Video Title'));
		$fields->addFieldToTab('Root.Main', new TextareaField('YouTubeCode', 'YouTube code to embed'));
		return $fields;
	}
	
}

?>

you can add more fields if you want.
Then just add $YouTubeCode in your template, as usual.