AC3 pass through has arrived..

See https://code.google.com/p/google-cast-sdk/issues/detail?id=192
But I can't get it to work. I've added a direct play video profile to the Chromecast profile of container="mkv" codec="h.264" audioCodec="ac3" but it's still transcoding to aac.
Stopped and started mediaserver multiple times, but no joy.
What am I missing? Running Windows 8.1

Thanks