I think I've found a bug in the ALSA reader filter - when I set the
reader to stereo mode I get "segmentation fault". I think it is a
buffer overflow problem. It happens even if the processing graph is very simple: just a reader and a void sink.
However, when I changed the size of allocated buffer in alsa_read_process() from: o = allocb(size,0) to o = allocb(size*ad->nchannels,0) it fixed the problem.