My favourite media server system is Emby and the Chromecast app has just had major update. The updated app has a new transcoding engine, the same as the Chrome browser version which has faster start times and reduced cpu utilisation.
There is a new Opus audio transcoding engine which has improved audio quality for aac and mp3 formats. There is full support for changing audio and subtitle tracks and there is automatic bitrate detection (based on available bandwidth).
All in all a nice set of updated that you will get by restarting the casting app.