The RadEditor InsertExternalVideo
dialog uses iframe to show the video.
In SharePoint usage of iframe elements is not recommenced and especially using it in an editable web part page could be restricted due to security reasons.
The iframe elemnts are not stripped from the RadEditor controls. You can this thread
for additional information.
In this Stackoverflow thread
is discussed the video sharing matter under SharePoint where some suggestions are provided. As an alternative, you can implement a custom tool
that adds a proper video that is supported in SharePoint.
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