Salesforce does not support Embedding Brainshark presentations in a Salesforce Knowledge Article (Salesforce Classic) There are two ways to work around this issue. (Lightning Only)
1. Get the Brainshark CRM Connector for Salesforce which has lightning components. The Brainshark Player component can be added to any Lightning Page. In the component settings there is a presentation URL text box where you would place the presentation's URL. If you do not have the Brainshark CRM Connector please contact your Company Admin or your Brainshark Account team to discuss licensing. If you have the Brainshark CRM Connector for Salesforce please contact support@bigtincan.com if assistance is needed
2. In Lightning you can add a visualforce component to the Lightning record page if you create a visual force component that iframes the Brainshark Presentation.
Example of Apex code for VisualForce page
<apex:page showHeader="false">
<apex:iframe src="https://www.brainshark.com/{logindir}/vu?pi=zGazuk9IzC7dWz0" > </apex:iframe>
</apex:page>
For each Brainshark presentation that you would like embedded on the page you will need to create a visualforce page for that presentation.