By default html from dam is blacklisted. Have you removed text/html
athttp://host:port/system/console/configMgr/com.day.cq.dam.core.impl.servlet.DamContentDispositionFilterOrhttp://host:port/system/console/configMgr/com.day.cq.dam.core.impl.servlet.SafeBinaryGetServlet
Hi Please have a look at this documentation,I hope this will help you:-
https://docs.adobe.com/docs/en/aem/6-1/administer/content/assets/video-transcoder.htmlThanks
and RegardsKautuk Sahni