Android and JS SDK are the first two SDKs supporting external output feature. Now Intel CS for WebRTC API for external output and recording features are under restructuring, this means they maybe changed in following releases. So such APIs stop to newly add temporarily. Thanks for your patience. If you have urgent business cases especially with Intel platforms, try to contact firstname.lastname@example.org to see whether there is any help can provide.
Currently , iOS sdk don't support addExternalOutput feature . Please be patient and waiting for following 4.0 version, we plan to do API refactoring for iOS sdk at 4.0 version .