All directives pointing to your endpoint [service URL as it's called at Kaltura] under /opt/kaltura/app/configurations/*ini should point to your LB over HTTPs.
Also, make sure your LB sets the X_FORWARDED_PROTO header to HTTPs. This is looked at here:
and, if set, the HTTPS ENV var is set to "on", which is what the code looks at to determine which protocol to use when making the requests [HTTP or HTTPs].
If you are still having issues, please state exactly where and use a HTTP sniffer to see exactly what requests are made over HTTP instead of going through your LB over HTTPs.
You can see all the requests your browser makes by opening your browser's dev tools and looking under the "Network" tab, also, check the "Console" tab for errors.