The client calls the methods in the IAudioRenderClient interface to write rendering data to an endpoint buffer. For a shared-mode stream, the client shares the endpoint buffer with the audio engine. For an exclusive-mode stream, the client shares the endpoint buffer with the audio device.
As far as I’m concerned WASAPI Renderer can play mono audio on both channels.
I suggest you could try to use IAudioClient::IsFormatSupported method indicates whether the audio endpoint device supports a particular stream format.
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