Module libpulse_binding::volume

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Expand description

Constants and routines for volume handling.

Overview

Sinks, sources, sink inputs, source outputs and samples can all have their own volumes. To deal with these, The PulseAudio library contains a number of functions that ease handling.

The basic volume type in PulseAudio is the Volume type. Most of the time, applications will use the aggregated ChannelVolumes structure that can store the volume of all channels at once.

Volumes commonly span between muted (0%), and normal (100%). It is possible to set volumes to higher than 100%, but clipping might occur.

There is no single well-defined meaning attached to the 100% volume for a sink input. In fact, it depends on the server configuration. With flat volumes enabled, it means the maximum volume that the sound hardware is capable of, which is usually so high that you absolutely must not set sink input volume to 100% unless the user explicitly requests that (note that usually you shouldn’t set the volume anyway if the user doesn’t explicitly request it, instead, let PulseAudio decide the volume for the sink input). With flat volumes disabled the sink input volume is relative to the sink volume, so 100% sink input volume means that the sink input is played at the current sink volume level. In this case 100% is often a good default volume for a sink input, although you still should let PulseAudio decide the default volume. It is possible to figure out whether flat volume mode is in effect for a given sink by calling Introspector::get_sink_info_by_name().

Calculations

The Volumes in PulseAudio are cubic in nature and applications should not perform calculations with them directly. Instead, they should be converted to and from either dB or a linear scale.

The VolumeDB type represents decibel (dB) converted values, and VolumeLinear, linear. The From trait has been implemented for your convenience, allowing such conversions.

For simple multiplication, Volume::multiply() and ChannelVolumes::sw_multiply() can be used.

It’s often unknown what scale hardware volumes relate to. Don’t use the above functions on sink and source volumes, unless the sink or source in question has the SinkFlagSet::DECIBEL_VOLUME or SourceFlagSet::DECIBEL_VOLUME flag set. The conversion functions are rarely needed anyway, most of the time it’s sufficient to treat all volumes as opaque with a range from Volume::MUTED (0%) to Volume::NORMAL (100%).

Structs

  • ChannelVolumes
    A structure encapsulating a per-channel volume
  • Volume
    Software volume expressed as an integer.
  • VolumeDB
    Software volume expressed in decibels (dBs).
  • VolumeLinear
    Software volume expressed as linear factor.

Constants