Mixing two sources with Adder

[Frédéric Praca]

Hello guys,
I would like to use two PulseAudio sources, one from the microphone and
one from a pipe using PulseAudio module-pipe-source.
In my Gstreamer pipeline, I use adder to "mix" the two sources.
The problem is that as long as the pipe source has not provided data,
the pipeline is blocked.
I was expecting the pipeline to deal with the microphone meanwhile,
even if I didn't write any data in the pipe.
Is there a way to mix two sources without blocking on one ?

Fred