[pulseaudio-discuss] Writing a volume meter

[flavio.ceolin at gmail.com]

Hi folks,

What is the best way to write a volume meter for a sink.
I've created a pa_stream and then connect it to the monitor_source of
the sink, but the data got in the read callback is always 0. The code is
pretty much the same of pavucontrol. Bellow are the two functions
involved:

static void
_read_cb(pa_stream *s, size_t length, void *userdata)
{
   const void *data;
   double v;

   if (pa_stream_peek(s, &data, &length) < 0)
     {
        printf("Failed to read data from stream\n");
        return;
     }

   SAFETY_ON_FALSE_RETURN(length > 0);
   SAFETY_ON_FALSE_RETURN(length % sizeof(float) == 0);

   v = ((const float*) data)[length / sizeof(float) -1];
   /* v is always 0 */

   pa_stream_drop(s);

   if (v < 0)
     v = 0;
   if (v > 1)
     v = 1;
   /*
    *TODO: update volume meter
    */
}

static void
_create_sink_monitor(Sink *si, unsigned int source_monitor)
{
   pa_stream *s;
   char t[16];
   pa_buffer_attr attr;
   pa_sample_spec ss;
   pa_stream_flags_t flags;

   if (si->peak)
     {
        pa_stream_disconnect(si->peak);
        si->peak = NULL;
     }

   ss.channels = 1;
   ss.format = PA_SAMPLE_FLOAT32;
   ss.rate = 25;

   memset(&attr, 0, sizeof(attr));
   attr.fragsize = sizeof(float);
   attr.maxlength = (uint32_t) -1;

   snprintf(t, sizeof(t), "%u", source_monitor);
   if (!(s = pa_stream_new(ctx->context, "Peak detect", &ss, NULL)))
     {
        printf("Failed to create monitoring stream\n");
        return;
     }

   pa_stream_set_read_callback(s, _read_cb, NULL);
   flags = (pa_stream_flags_t) (PA_STREAM_DONT_MOVE | PA_STREAM_PEAK_DETECT |
                                PA_STREAM_ADJUST_LATENCY | PA_STREAM_NOFLAGS);

   if (pa_stream_connect_record(s, t, &attr, flags) < 0)
     {
        printf("Failed to connect monitoring stream\n");
        pa_stream_unref(s);
        return;
     }

   si->peak = s;
}

Apparently it's not working on pavucontrol as well. I also tried to
check the pavumeter but the repository where it is seems to be down.


Regards,
Flavio Ceolin