Bus Message Structure

Brian Duffy brduffy at gmail.com
Thu Mar 22 13:36:18 PDT 2012


I am trying to use CMU's PocketSphinx plugin for Gstreamer from Vala and I
am running into a problem getting access to the message structure in my bus
callback function (app_message). For some reason when I use the
get_structure method to return the structure of the message and then call a
method on that structure such as get_name() or get_string(), I get a
critical Gstreamer error :

(cmu:26958): GStreamer-CRITICAL **: gst_structure_get_string: assertion
`structure != NULL' failed

I just can't figure out why my message structure would be null. Any ideas?
Here is my code ...

using Gst;

class Sphinx : GLib.Object {

// experimenting with gstreamer pocketsphinx
private Gst.Pipeline pipeline;
private Gst.Element vader;
dynamic Gst.Element asr;
private Gst.Bus bus;
private Gst.Structure msg;
private Gst.Structure my_struct;
private Gst.Structure my_struct2;
private Gst.Message message;

private MainLoop loop;

public Sphinx() {

 string a = """pulsesrc
device="alsa_input.usb-AKM_AK5370-00-AK5370.analog-mono" ! audioconvert
string b = """ audioresample ! vader name=vad auto-threshold=true !
pocketsphinx name=asr ! fakesink""";

string pipeDef = a + b;

try {
pipeline = (Pipeline)Gst.parse_launch(pipeDef);
} catch (Error e) {
stdout.printf("Error: %s\n", e.message);
 bus = pipeline.get_bus();

asr = pipeline.get_by_name("asr");

asr.set_property("lm", "4038.lm");
                asr.set_property("dict", "4038.dic");


asr.set_property("configured", true);

bus = pipeline.get_bus();


loop = new MainLoop ();


private void asrPartialResult(Gst.Element asr, string text, string uttid) {
              my_struct = new Gst.Structure.empty("partial_result");

              my_struct.set_value("hyp", text);
              my_struct.set_value("uttid", uttid);

              asr.post_message(new Gst.Message.application(asr, my_struct));

private void asrResult(Gst.Element asr, string text, string uttid) {

//stdout.printf("%s", "inside asrResult");
               my_struct2 = new Gst.Structure.empty("result");

               my_struct2.set_value("hyp", text);
               my_struct2.set_value("uttid", uttid);

               asr.post_message(new Gst.Message.application(asr,

private void app_message(Gst.Bus bus, Gst.Message p_msg) {
 // trying to get the string that PocketSphinx converts my voice to here
// but I keep getting : GStreamer-CRITICAL **: gst_structure_get_string:
assertion `structure != NULL' failed

string msg_string = p_msg.get_structure().get_string("hyp");
 /* // Not using any of this for now
if (msgType == null) {
stdout.printf("%s", "null");
stdout.printf("%s", "not null");

//stdout.printf("%s", msgType);

//if (p_msg.type == MessageType.APPLICATION) {
// stdout.printf("%s", "booyah");

if (msg["hyp"]) {
stdout.printf("%s", "true");
stdout.printf("%s", "false");

if (msgType == "partial_result") {
//partialResult(msg["hyp"], msg["uttid"]);
}else if (msgType == "result") {
//finalResult(msg["hyp"], msg["uttid"]);
//return true;

private void partialResult(GLib.Value hyp, GLib.Value uttid) {

stdout.printf("%s", (string)hyp);

private void finalResult(GLib.Value hyp, GLib.Value uttid) {
stdout.printf("%s", (string)hyp);


int main (string[] args) {

Gst.init(ref args);

var sphinx = new Sphinx();

return 0;

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