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;
}
Hierarchy
GObject ╰──GInitiallyUnowned ╰──GstObject ╰──GstElement ╰──GstBaseTransform ╰──GstAudioFilter ╰──spectrum
Factory details
Authors: – Erik Walthinsen
Classification: – Filter/Analyzer/Audio
Rank – none
Plugin – spectrum
Package – GStreamer Good Plug-ins
Pad Templates
sink
audio/x-raw:
format: { S16LE, S24LE, S32LE, F32LE, F64LE }
rate: [ 1, 2147483647 ]
channels: [ 1, 2147483647 ]
layout: interleaved
src
audio/x-raw:
format: { S16LE, S24LE, S32LE, F32LE, F64LE }
rate: [ 1, 2147483647 ]
channels: [ 1, 2147483647 ]
layout: interleaved
Properties
interval
“interval” guint64
Interval of time between message posts (in nanoseconds)
Flags : Read / Write
Default value : 100000000
message-magnitude
“message-magnitude” gboolean
Whether to add a 'magnitude' field to the structure of any 'spectrum' element messages posted on the bus
Flags : Read / Write
Default value : true
message-phase
“message-phase” gboolean
Whether to add a 'phase' field to the structure of any 'spectrum' element messages posted on the bus
Flags : Read / Write
Default value : false
multi-channel
“multi-channel” gboolean
Send separate results for each channel
Flags : Read / Write
Default value : false
post-messages
“post-messages” gboolean
Whether to post a 'spectrum' element message on the bus for each passed interval
Flags : Read / Write
Default value : true
threshold
“threshold” gint
dB threshold for result. All lower values will be set to this
Flags : Read / Write
Default value : -60
The results of the search are