See: https://github.com/kaltura/mwEmbed/blob/v2.48.1/modules/Hlsjs/resources/hlsjs.js#L5
You can try to change that condition and clear /opt/kaltura/web/html5/html5lib/v2.48.1/cache/*
But again, I strongly recommend you DO use HLS instead of progressive. What is the reason for your host refusing the use of Nginx?