level

level

Properties

guint64 interval Read / Write
gboolean message Read / Write
gdouble peak-falloff Read / Write
guint64 peak-ttl Read / Write
gboolean post-messages Read / Write

Types and Values

struct GstLevel

Object Hierarchy

    GObject
    ╰── GInitiallyUnowned
        ╰── GstObject
            ╰── GstElement
                ╰── GstBaseTransform
                    ╰── GstLevel

Description

Level analyses incoming audio buffers and, if the “message” property is TRUE, generates an element message named

"level":

after each interval of time given by the “interval” property. The message's structure contains 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)

  • GValueArray of gdouble "peak": the peak power level in dB for each channel

  • GValueArray of gdouble "decay": the decaying peak power level in dB for each channel The decaying peak level follows the peak level, but starts dropping if no new peak is reached after the time given by the “peak-ttl”. When the decaying peak level drops, it does so at the decay rate as specified by the “peak-falloff”.

  • GValueArray of gdouble "rms": the Root Mean Square (or average power) level in dB for each channel

Example application

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
/* GStreamer
 * Copyright (C) 2000,2001,2002,2003,2005
 *           Thomas Vander Stichele <thomas at apestaart dot org>
 *
 * 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 <string.h>
#include <math.h>

#define GLIB_DISABLE_DEPRECATION_WARNINGS

#include <gst/gst.h>

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);

    if (strcmp (name, "level") == 0) {
      gint channels;
      GstClockTime endtime;
      gdouble rms_dB, peak_dB, decay_dB;
      gdouble rms;
      const GValue *array_val;
      const GValue *value;
      GValueArray *rms_arr, *peak_arr, *decay_arr;
      gint i;

      if (!gst_structure_get_clock_time (s, "endtime", &endtime))
        g_warning ("Could not parse endtime");

      /* the values are packed into GValueArrays with the value per channel */
      array_val = gst_structure_get_value (s, "rms");
      rms_arr = (GValueArray *) g_value_get_boxed (array_val);

      array_val = gst_structure_get_value (s, "peak");
      peak_arr = (GValueArray *) g_value_get_boxed (array_val);

      array_val = gst_structure_get_value (s, "decay");
      decay_arr = (GValueArray *) g_value_get_boxed (array_val);

      /* we can get the number of channels as the length of any of the value
       * arrays */
      channels = rms_arr->n_values;
      g_print ("endtime: %" GST_TIME_FORMAT ", channels: %d\n",
          GST_TIME_ARGS (endtime), channels);
      for (i = 0; i < channels; ++i) {

        g_print ("channel %d\n", i);
        value = g_value_array_get_nth (rms_arr, i);
        rms_dB = g_value_get_double (value);

        value = g_value_array_get_nth (peak_arr, i);
        peak_dB = g_value_get_double (value);

        value = g_value_array_get_nth (decay_arr, i);
        decay_dB = g_value_get_double (value);
        g_print ("    RMS: %f dB, peak: %f dB, decay: %f dB\n",
            rms_dB, peak_dB, decay_dB);

        /* converting from dB to normal gives us a value between 0.0 and 1.0 */
        rms = pow (10, rms_dB / 20);
        g_print ("    normalized rms value: %f\n", rms);
      }
    }
  }
  /* we handled the message we want, and ignored the ones we didn't want.
   * so the core can unref the message for us */
  return TRUE;
}

int
main (int argc, char *argv[])
{
  GstElement *audiotestsrc, *audioconvert, *level, *fakesink;
  GstElement *pipeline;
  GstCaps *caps;
  GstBus *bus;
  guint watch_id;
  GMainLoop *loop;

  gst_init (&argc, &argv);

  caps = gst_caps_from_string ("audio/x-raw,channels=2");

  pipeline = gst_pipeline_new (NULL);
  g_assert (pipeline);
  audiotestsrc = gst_element_factory_make ("audiotestsrc", NULL);
  g_assert (audiotestsrc);
  audioconvert = gst_element_factory_make ("audioconvert", NULL);
  g_assert (audioconvert);
  level = gst_element_factory_make ("level", NULL);
  g_assert (level);
  fakesink = gst_element_factory_make ("fakesink", NULL);
  g_assert (fakesink);

  gst_bin_add_many (GST_BIN (pipeline), audiotestsrc, audioconvert, level,
      fakesink, NULL);
  if (!gst_element_link (audiotestsrc, audioconvert))
    g_error ("Failed to link audiotestsrc and audioconvert");
  if (!gst_element_link_filtered (audioconvert, level, caps))
    g_error ("Failed to link audioconvert and level");
  if (!gst_element_link (level, fakesink))
    g_error ("Failed to link level and fakesink");

  /* make sure we'll get messages */
  g_object_set (G_OBJECT (level), "post-messages", TRUE, NULL);
  /* run synced and not as fast as we can */
  g_object_set (G_OBJECT (fakesink), "sync", TRUE, NULL);

  bus = gst_element_get_bus (pipeline);
  watch_id = gst_bus_add_watch (bus, message_handler, NULL);

  gst_element_set_state (pipeline, 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);

  g_source_remove (watch_id);
  g_main_loop_unref (loop);
  return 0;
}

Synopsis

Element Information

plugin

level

author

Thomas Vander Stichele <thomas at apestaart dot org>

class

Filter/Analyzer/Audio

Element Pads

name

sink

direction

sink

presence

always

details

audio/x-raw, format=(string){ S8, S16LE, S32LE, F32LE, F64LE }, layout=(string)interleaved, rate=(int)[ 1, 2147483647 ], channels=(int)[ 1, 2147483647 ]

name

src

direction

source

presence

always

details

audio/x-raw, format=(string){ S8, S16LE, S32LE, F32LE, F64LE }, layout=(string)interleaved, rate=(int)[ 1, 2147483647 ], channels=(int)[ 1, 2147483647 ]

Functions

Types and Values

struct GstLevel

struct GstLevel;

Opaque data structure.

Property Details

The “interval” property

  “interval”                 guint64

Interval of time between message posts (in nanoseconds).

Flags: Read / Write

Allowed values: >= 1

Default value: 100000000


The “message” property

  “message”                  gboolean

Post a 'level' message for each passed interval (deprecated, use the post-messages property instead).

Flags: Read / Write

Default value: TRUE


The “peak-falloff” property

  “peak-falloff”             gdouble

Decay rate of decay peak after TTL (in dB/sec).

Flags: Read / Write

Allowed values: >= 0

Default value: 10


The “peak-ttl” property

  “peak-ttl”                 guint64

Time To Live of decay peak before it falls back (in nanoseconds).

Flags: Read / Write

Default value: 300000000


The “post-messages” property

  “post-messages”            gboolean

Post messages on the bus with level information.

GstLevel:post-messages is deprecated and should not be used in newly-written code.

use the “post-messages” property

Flags: Read / Write

Default value: TRUE

Since: 1.1.0