Are there any technical details available about the stream format, uri, port, etc. that are used with the "private listening" feature? Is it a regular MP3 style radio stream, or RTSP/RTP or similar? Or is it something proprietary? How would one implement the private listening feature in their own application?
I see that the ECP rest api gives a "supports-private-listening" boolean
"Private listening" is a feature available by plugging headphones into your Roku remote or with your mobile phone connected to your Roku with the Roku mobile app. Any audio that is played on a Roku will be redirected to your headphones if connected by either method (not both at the same time). I don't think there is a way to access it any other way. It is not something that developers have access to. depending on the Roku model it may be a blutooth or wifi direct connection to the remote. I have not encountered any documentation that indicates what transfer method the stream is sent as.
I also, would like to have this information. I intend to use it to play the sound through assistive hearing devices as I suffer from a hearing disability. I sure hope roku is cooperative in accommodating Americans with disabilities by sharing how the app connects for 'private listening'.
I did some investigation and found it uses WebSockets to set audio to stream to an RTP port. That could be useful. However, the WebSocket session starts with an auth challenge and required response that appears designed to prevent anyone using this mechanism without having a some sort of secret password or certificate. Thus, without dev support from Roku, unfortunately I believe it is not possible to access this feature.