spectrum

The Spectrum element analyzes the frequency spectrum of an audio signal. If the GstSpectrum:post-messages property is TRUE, it sends analysis results as element messages named spectrum after each interval of time given by the GstSpectrum:interval property.

The message's structure contains some combination of these fields:

• GstClockTime timestamp: the timestamp of the buffer that triggered the message.
• GstClockTime stream-time: the stream time of the buffer.
• GstClockTime running-time: the running_time of the buffer.
• GstClockTime duration: the duration of the buffer.
• GstClockTime endtime: the end time of the buffer that triggered the message as stream time (this is deprecated, as it can be calculated from stream-time + duration)
• A GST_TYPE_LIST value of gfloat magnitude: the level for each frequency band in dB. All values below the value of the GstSpectrum:threshold property will be set to the threshold. Only present if the GstSpectrum:message-magnitude property is TRUE.
• A GST_TYPE_LIST of gfloat phase: The phase for each frequency band. The value is between -pi and pi. Only present if the GstSpectrum:message-phase property is TRUE.

If GstSpectrum:multi-channel property is set to true. magnitude and phase fields will be each a nested GST_TYPE_ARRAY value. The first dimension are the channels and the second dimension are the values.

Example application

/* GStreamer
 * Copyright (C) 2006 Stefan Kost <ensonic@users.sf.net>
 * Copyright (C) 2008 Jan Schmidt <jan.schmidt@sun.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <gst/gst.h>

static guint spect_bands = 20;

#define AUDIOFREQ 32000

/* receive spectral data from element message */
static gboolean
message_handler (GstBus * bus, GstMessage * message, gpointer data)
{
  if (message->type == GST_MESSAGE_ELEMENT) {
    const GstStructure *s = gst_message_get_structure (message);
    const gchar *name = gst_structure_get_name (s);
    GstClockTime endtime;

    if (strcmp (name, "spectrum") == 0) {
      const GValue *magnitudes;
      const GValue *phases;
      const GValue *mag, *phase;
      gdouble freq;
      guint i;

      if (!gst_structure_get_clock_time (s, "endtime", &endtime))
        endtime = GST_CLOCK_TIME_NONE;

      g_print ("New spectrum message, endtime %" GST_TIME_FORMAT "\n",
          GST_TIME_ARGS (endtime));

      magnitudes = gst_structure_get_value (s, "magnitude");
      phases = gst_structure_get_value (s, "phase");

      for (i = 0; i < spect_bands; ++i) {
        freq = (gdouble) ((AUDIOFREQ / 2) * i + AUDIOFREQ / 4) / spect_bands;
        mag = gst_value_list_get_value (magnitudes, i);
        phase = gst_value_list_get_value (phases, i);

        if (mag != NULL && phase != NULL) {
          g_print ("band %d (freq %g): magnitude %f dB phase %f\n", i, freq,
              g_value_get_float (mag), g_value_get_float (phase));
        }
      }
      g_print ("\n");
    }
  }
  return TRUE;
}

int
main (int argc, char *argv[])
{
  GstElement *bin;
  GstElement *src, *audioconvert, *spectrum, *sink;
  GstBus *bus;
  GstCaps *caps;
  GMainLoop *loop;

  gst_init (&argc, &argv);

  bin = gst_pipeline_new ("bin");

  src = gst_element_factory_make ("audiotestsrc", "src");
  g_object_set (G_OBJECT (src), "wave", 0, "freq", 6000.0, NULL);
  audioconvert = gst_element_factory_make ("audioconvert", NULL);
  g_assert (audioconvert);

  spectrum = gst_element_factory_make ("spectrum", "spectrum");
  g_object_set (G_OBJECT (spectrum), "bands", spect_bands, "threshold", -80,
      "post-messages", TRUE, "message-phase", TRUE, NULL);

  sink = gst_element_factory_make ("fakesink", "sink");
  g_object_set (G_OBJECT (sink), "sync", TRUE, NULL);

  gst_bin_add_many (GST_BIN (bin), src, audioconvert, spectrum, sink, NULL);

  caps = gst_caps_new_simple ("audio/x-raw",
      "rate", G_TYPE_INT, AUDIOFREQ, NULL);

  if (!gst_element_link (src, audioconvert) ||
      !gst_element_link_filtered (audioconvert, spectrum, caps) ||
      !gst_element_link (spectrum, sink)) {
    fprintf (stderr, "can't link elements\n");
    exit (1);
  }
  gst_caps_unref (caps);

  bus = gst_element_get_bus (bin);
  gst_bus_add_watch (bus, message_handler, NULL);
  gst_object_unref (bus);

  gst_element_set_state (bin, GST_STATE_PLAYING);

  /* we need to run a GLib main loop to get the messages */
  loop = g_main_loop_new (NULL, FALSE);
  g_main_loop_run (loop);

  gst_element_set_state (bin, GST_STATE_NULL);

  gst_object_unref (bin);

  return 0;
}

audio/x-raw:
         format: { S16LE, S24LE, S32LE, F32LE, F64LE }
           rate: [ 1, 2147483647 ]
       channels: [ 1, 2147483647 ]
         layout: interleaved

audio/x-raw:
         format: { S16LE, S24LE, S32LE, F32LE, F64LE }
           rate: [ 1, 2147483647 ]
       channels: [ 1, 2147483647 ]
         layout: interleaved