How to play custom audio for speech bot?

[Vivihung]

Hi all,

I would like to create a bot which can play audio (e.g., podcast, mp3, ...) during a voice conversation. (don't want to use media attachment of messages)
I've enabled cognitive service for my bot for text-to-speech and speech-to-text. The next step is to create a custom action which could return streaming.
However, based on the C# function signature, I'm not sure if streaming output is supported in custom dialog/actions.
No luck in finding related sample code.

Any help is appreciated. Thanks!