Loopback

The loopback module passes the output of a capture stream unmodified to a playback stream. It can be used to construct a link between a source and sink but also to create new virtual sinks or sources or to remap channel between streams.

Because both ends of the loopback are built with streams, the session manager can manage the configuration and connection with the sinks and sources.

Module Name

libpipewire-module-loopback

Module Options

• node.description: a human readable name for the loopback streams
• target.delay.sec: delay in seconds as float (Since 0.3.60)
• capture.props = {}: properties to be passed to the input stream
• playback.props = {}: properties to be passed to the output stream

General options

Options with well-known behavior. Most options can be added to the global configuration or the individual streams:

• PW_KEY_REMOTE_NAME
• PW_KEY_AUDIO_RATE
• PW_KEY_AUDIO_CHANNELS
• SPA_KEY_AUDIO_POSITION
• PW_KEY_MEDIA_NAME
• PW_KEY_NODE_LATENCY
• PW_KEY_NODE_DESCRIPTION
• PW_KEY_NODE_GROUP
• PW_KEY_NODE_LINK_GROUP
• PW_KEY_NODE_VIRTUAL
• PW_KEY_NODE_NAME: See notes below. If not specified, defaults to 'loopback-<pid>-<module-id>'.

Stream only properties:

• PW_KEY_MEDIA_CLASS
• PW_KEY_NODE_NAME: if not given per stream, the global node.name will be prefixed with 'input.' and 'output.' to generate a capture and playback stream node.name respectively.

Example configuration of a virtual sink

This Virtual sink routes stereo input to the rear channels of a 7.1 sink.

context.modules = [
{   name = libpipewire-module-loopback
    args = {
        node.description = "CM106 Stereo Pair 2"
        #target.delay.sec = 1.5
        capture.props = {
            node.name = "CM106_stereo_pair_2"
            media.class = "Audio/Sink"
            audio.position = [ FL FR ]
        }
        playback.props = {
            node.name = "playback.CM106_stereo_pair_2"
            audio.position = [ RL RR ]
            target.object = "alsa_output.usb-0d8c_USB_Sound_Device-00.analog-surround-71"
            node.dont-reconnect = true
            stream.dont-remix = true
            node.passive = true
        }
    }
}
]

Example configuration of a virtual source

This Virtual source routes the front-left channel of a multi-channel input to a mono channel. This is useful for splitting up multi-channel inputs from USB audio interfaces that are not yet fully supported by alsa.

context.modules = [
{   name = libpipewire-module-loopback
    args = {
      node.description = "Scarlett Focusrite Line 1"
      capture.props = {
          audio.position = [ FL ]
          stream.dont-remix = true
          node.target = "alsa_input.usb-Focusrite_Scarlett_Solo_USB_Y7ZD17C24495BC-00.analog-stereo"
          node.passive = true
      }
      playback.props = {
          node.name = "SF_mono_in_1"
          media.class = "Audio/Source"
          audio.position = [ MONO ]
      }
    }
}
]

See also

pw-loopback : a tool that loads the loopback module with given parameters.