Pulseaudio C API: create a null sink

Question

I am trying to create 2 simple programs that are basically the parec-simple and pacat-simple examples from the pulseaudio documentation. The only difference is that I would like to create a null sink, equivalent of

pactl load-module module-null-sink sink_name=steam

(see example here) which I would then use instead of the default device on both ends - playback and record.

My question is: how can I create this null sink using pulseaudio's C API? From what I saw, pulse/simple.h does not contain any function definition to do this, so I guess I would have to use libpulse.

Hey Copil, did you find a way to do it? – Barthy Jan 15 '21 at 22:21 — Barthy, Jan 15 '21 at 22:21
@Barthy: yes, see the answer below. – Copil tembel Jan 17 '21 at 10:03 — Copil tembel, Jan 17 '21 at 10:03

score 1 · Accepted Answer · answered Jan 17 '21 at 10:02

I couldn't find the pulseaudio API for it so I just use the pactl interface directly.

For anyone interested, here is a sample code that worked for me. I just used popen to execute the pactl command to create a (null) sink:

static bool createNullPaSink(const std::string& sinkName, int* paHandleId) {

    // this is the command to create the null sink with some specific setup (format, channels, rate, etc.0
    std::string pacmd = "pactl load-module module-null-sink latency_msec=100 format=s16le rate=48000 channels=2 channel_map=front-left,front-right sink_properties=device.description=QM sink_name=" + sinkName;
    // execute the pactl command
    FILE* f = popen(pacmd.c_str(), "r");
    if (!f) {
        // creating the sink failed
        return false;
    }
    
    // now get the handle of the sink by reading the output of the popen command above
    std::array<char, 128> buffer;
    std::string spaHandleId;
    while (fgets(buffer.data(), 128, f) != NULL) {
        spaHandleId += buffer.data();
    }
    auto returnCode = pclose(f);
    if (returnCode) {
        return false;
    }

    *paHandleId = std::stoi(spaHandleId);
    
    return true;
}

Pulseaudio C API: create a null sink

1 Answers1