gststreamvolume

## gststreamvolume gststreamvolume — Interface for elements that provide a stream volume |

## Synopsis

    #include <gst/audio/streamvolume.h>

                        GstStreamVolume;
    enum                GstStreamVolumeFormat;
    gdouble             gst_stream_volume_get_volume        (GstStreamVolume *volume,
                                                             GstStreamVolumeFormat format);
    void                gst_stream_volume_set_volume        (GstStreamVolume *volume,
                                                             GstStreamVolumeFormat format,
                                                             gdouble val);
    gboolean            gst_stream_volume_get_mute          (GstStreamVolume *volume);
    void                gst_stream_volume_set_mute          (GstStreamVolume *volume,
                                                             gboolean mute);
    gdouble             gst_stream_volume_convert_volume    (GstStreamVolumeFormat from,
                                                             GstStreamVolumeFormat to,
                                                             gdouble val);

## Object Hierarchy

      GInterface
       +----GstStreamVolume

## Prerequisites

GstStreamVolume requires GObject.

## Properties

      "mute"                     gboolean              : Read / Write
      "volume"                   gdouble               : Read / Write

## Description

This interface is implemented by elements that provide a stream volume. Examples for such elements are volume and playbin.

Applications can use this interface to get or set the current stream volume. For this the "volume" GObject property can be used or the helper functions `gst_stream_volume_set_volume()` and `gst_stream_volume_get_volume()`. This volume is always a linear factor, i.e. 0.0 is muted 1.0 is 100%. For showing the volume in a GUI it might make sense to convert it to a different format by using `gst_stream_volume_convert_volume()`. Volume sliders should usually use a cubic volume.

Separate from the volume the stream can also be muted by the "mute" GObject property or `gst_stream_volume_set_mute()` and `gst_stream_volume_get_mute()`.

Elements that provide some kind of stream volume should implement the "volume" and "mute" GObject properties and handle setting and getting of them properly. The volume property is defined to be a linear volume factor.

## Details

### GstStreamVolume

    typedef struct _GstStreamVolume GstStreamVolume;

### enum GstStreamVolumeFormat

    typedef enum {
      GST_STREAM_VOLUME_FORMAT_LINEAR = 0,
      GST_STREAM_VOLUME_FORMAT_CUBIC,
      GST_STREAM_VOLUME_FORMAT_DB
    } GstStreamVolumeFormat;

Different representations of a stream volume. `gst_stream_volume_convert_volume()` allows to convert between the different representations.

Formulas to convert from a linear to a cubic or dB volume are cbrt(val) and 20 * log10 (val).

`GST_STREAM_VOLUME_FORMAT_LINEAR` | Linear scale factor, 1.0 = 100%
`GST_STREAM_VOLUME_FORMAT_CUBIC` | Cubic volume scale
`GST_STREAM_VOLUME_FORMAT_DB` | Logarithmic volume scale (dB, amplitude not power)

### gst_stream_volume_get_volume ()

    gdouble             gst_stream_volume_get_volume        (GstStreamVolume *volume,
                                                             GstStreamVolumeFormat format);

`volume` : | GstStreamVolume that should be used
`format` : | GstStreamVolumeFormat which should be returned
Returns : | The current stream volume as linear factor

### gst_stream_volume_set_volume ()

    void                gst_stream_volume_set_volume        (GstStreamVolume *volume,
                                                             GstStreamVolumeFormat format,
                                                             gdouble val);

`volume` : | GstStreamVolume that should be used
`format` : | GstStreamVolumeFormat of `val`
`val` : | Linear volume factor that should be set

### gst_stream_volume_get_mute ()

    gboolean            gst_stream_volume_get_mute          (GstStreamVolume *volume);

`volume` : | GstStreamVolume that should be used
Returns : | Returns `TRUE` if the stream is muted

### gst_stream_volume_set_mute ()

    void                gst_stream_volume_set_mute          (GstStreamVolume *volume,
                                                             gboolean mute);

`volume` : | GstStreamVolume that should be used
`mute` : | Mute state that should be set

### gst_stream_volume_convert_volume ()

    gdouble             gst_stream_volume_convert_volume    (GstStreamVolumeFormat from,
                                                             GstStreamVolumeFormat to,
                                                             gdouble val);

`from` : | GstStreamVolumeFormat to convert from
`to` : | GstStreamVolumeFormat to convert to
`val` : | Volume in `from` format that should be converted
Returns : | the converted volume

## Property Details

### The `"mute"` property

      "mute"                     gboolean              : Read / Write

Mute the audio channel without changing the volume.

Default value: FALSE

### The `"volume"` property

      "volume"                   gdouble               : Read / Write

Linear volume factor, 1.0=100%.

Allowed values: >= 0

Default value: 1