[pulseaudio-discuss] How to create a virtual microphone with source set as default monitor device?

[Sean Greenslade]

On Sun, Sep 13, 2020 at 05:18:23PM +0000, guest271314 wrote:
> This project started attempting to capture the output of
> window.speechSynthesis.speak().
> 
> Consider https://stackoverflow.com/a/43553706.
> 
> If run $ pacmd list-sink-inputs will get
> 
>     index: 219
>     driver: <protocol-native.c>
>     flags:
>     state: RUNNING
>     sink: 4 <alsa_output.pci-0000_00_14.2.analog-stereo>
>     volume: mono: 64460 /  98% / -0.43 dB
>             balance 0.00
>     muted: no
>     current latency: 0.00 ms
>     requested latency: 0.59 ms
>     sample spec: s16le 1ch 22050Hz
>     channel map: mono
>                  Mono
>     resample method: speex-float-1
>     module: 14
>     client: 192 <speech-dispatcher-espeak-ng>
>     properties:
>         media.name = "playback"
>         application.name = "speech-dispatcher-espeak-ng"
>         native-protocol.peer = "UNIX socket client"
>         native-protocol.version = "33"
>         application.process.id = "45464"
>         application.process.user = "ubuntu-studio"
>         application.process.host = "ubuntu-studio"
>         application.process.binary = "sd_espeak-ng"
>         application.language = "C"
>         window.x11.display = ":0.0"
>         application.process.machine_id = "<id>"
>         application.process.session_id = "<id>"
>         module-stream-restore.id =
> "sink-input-by-application-name:speech-dispatcher-espeak-ng"
> 
> $ pacmd list-sources
> 
> 2 source(s) available.
>   * index: 4
>     name: <alsa_input.usb-046d_0804_0B17FC60-02.mono-fallback>
>     driver: <module-alsa-card.c>
>     flags: HARDWARE HW_MUTE_CTRL HW_VOLUME_CTRL DECIBEL_VOLUME LATENCY
> DYNAMIC_LATENCY
>     state: RUNNING
>     suspend cause: (none)
>     priority: 9040
>     volume: mono: 0 /   0% / -inf dB
>             balance 0.00
>     base volume: 20724 /  32% / -30.00 dB
>     volume steps: 65537
>     muted: yes
>     current latency: 4.60 ms
>     max rewind: 0 KiB
>     sample spec: s16le 1ch 48000Hz
>     channel map: mono
>                  Mono
>     used by: 1
>     linked by: 1
>     configured latency: 40.00 ms; range is 0.50 .. 2000.00 ms
>     card: 1 <alsa_card.usb-046d_0804_0B17FC60-02>
>     module: 8
>     properties:
>         alsa.resolution_bits = "16"
>         device.api = "alsa"
>         device.class = "sound"
>         alsa.class = "generic"
>         alsa.subclass = "generic-mix"
>         alsa.name = "USB Audio"
>         alsa.id = "USB Audio"
>         alsa.subdevice = "0"
>         alsa.subdevice_name = "subdevice #0"
>         alsa.device = "0"
>         alsa.card = "1"
>         alsa.card_name = "USB Device 0x46d:0x804"
>         alsa.long_card_name = "USB Device 0x46d:0x804 at
> usb-0000:00:12.0-1.4, high speed"
>         alsa.driver_name = "snd_usb_audio"
>         device.bus_path = "pci-0000:00:12.0-usb-0:1.4:1.2"
>         sysfs.path =
> "/devices/pci0000:00/0000:00:12.0/usb1/1-1/1-1.4/1-1.4:1.2/sound/card1"
>         udev.id = "usb-046d_0804_0B17FC60-02"
>         device.bus = "usb"
>         device.vendor.id = "046d"
>         device.vendor.name = "<vendor>"
>         device.product.id = "0804"
>         device.product.name = "<name>"
>         device.serial = "046d_0804_0B17FC60"
>         device.form_factor = "webcam"
>         device.string = "hw:1"
>         device.buffering.buffer_size = "192000"
>         device.buffering.fragment_size = "96000"
>         device.access_mode = "mmap+timer"
>         device.profile.name = "mono-fallback"
>         device.profile.description = "Mono"
>         device.description = "<description>"
>         module-udev-detect.discovered = "1"
>         device.icon_name = "camera-web-usb"
>     ports:
>         analog-input-mic: Microphone (priority 8700, latency offset 0
> usec, available: unknown)
>             properties:
>                 device.icon_name = "audio-input-microphone"
>     active port: <analog-input-mic>
> 
> One part of what am trying to do is create a virtual microphone that
> takes input from speech-dispatcher-espeak-ng persistently or route
> output from speech-dispatcher-espeak-ng to the microphone, so that
> when capture the microphone the output will be from speech-dispatcher.
> How to achieve that?

$ pacmd load-module module-null-sink sink_name=feed_espeak_to_me
$ pacmd update-sink-proplist feed_espeak_to_me device.description="\"Feed Espeak\""
$ pacmd update-source-proplist virtual_mic_espeak_output device.description="\"ESpeak output virtual mic\""

Point Espeak's output to the "Feed Espeak" sink, and point your
recording application at the "ESpeak output virtual mic".

--Sean