TPE-SFO on a 777-300,
Asked a FA to ask the captain about ch 9. He comes back and shakes my hand saying he'd be glad to. Said plane is brand new though so he's not sure if it works, but that there was a switch in the cockpit and to let him know at the end of the flight. Then goes on to make a cabin announcement about it.
In seat entertainment system has a "from the flight deck" option. Tried multiple seats.
Sadly, no audio. Oh well.