A Weird Imagination

Virtual microphone using GStreamer and PulseAudio

The problem

My previous post got the video from my smartphone to show up as a camera device on my desktop, but for a video chat, we probably also want audio. So, now the question is: how to build GStreamer pipelines that will allow minimal-webrtc-gstreamer to use virtual microphone and speaker devices that I can point a voice/video chat application at, allowing me to use my smartphone's microphone and speaker for applications on my desktop.

The solution

The following requires that you are using PulseAudio as your sound server and have downloaded minimal-webrtc-gstreamer:

pactl load-module module-null-sink sink_name=virtspk \
    sink_properties=device.description=Virtual_Speaker
pactl load-module module-null-sink sink_name=virtmic \
    sink_properties=device.description=Virtual_Microphone_Sink
pactl load-module module-remap-source \
    master=virtmic.monitor source_name=virtmic \
    source_properties=device.description=Virtual_Microphone
./minimal-webrtc-host.py\
    --url "https://apps.aweirdimagination.net/camera/"\
    --receiveAudioTo device=virtmic\
    --sendAudio "pulsesrc device=virtspk.monitor"\
    --sendVideo false --receiveVideo false

You can reset your PulseAudio configuration by killing PulseAudio:

pulseaudio -k

You can make the PulseAudio settings permanent by following these instructions to put them in your default.pa file.

The details

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Virtual web cam using GStreamer and v4l2loopback

The problem

I want to make my smartphone's camera appear as an actual camera device on my desktop so any application (primarily Discord) can use it like it were a normal USB web cam.

My previous post introduced minimal-webrtc-gstreamer, which got as far as getting the video stream from any web browser into a GStreamer pipeline, which reduces the problem to outputting a GStreamer pipeline into a virtual web cam device.

The solution

Download minimal-webrtc-gstreamer and install v4l2loopback. Then run

sudo modprobe v4l2loopback video_nr="42"\
    'card_label=virtcam'\
    exclusive_caps=1 max_buffers=2
./minimal-webrtc-host.py\
    --url "https://apps.aweirdimagination.net/camera/"\
    --receiveVideoTo /dev/video42\
    --sendAudio false

You can test by watching the stream with

gst-launch-1.0 v4l2src device=/dev/video42 ! autovideosink

Note that some applications, including the current desktop release of Discord may not support the virtual camera, showing a solid black square or failing to connect to it at all. It should work in the latest Chromium/Chrome browser, including for the Discord web app.

When done, remove the virtual camera device:

sudo modprobe -r v4l2loopback

The details

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GStreamer WebRTC

The problem

In my previous posts on minimal-webrtc, I set up a peer-to-peer connection between the web browsers on two different devices. For more flexibility, including making the remote camera and microphone appear as local camera and microphone devices, we need to handle the WebRTC connection outside of a web browser.

The solution

minimal-webrtc-gstreamer is a command-line client for minimal-webrtc written in Python using the GStreamer library. It's mostly a modification of the webrtc-sendrecv.py demo script to use minimal-webrtc as the signaling server to make it easier for me to tinker with.

Run as follows:

./minimal-webrtc-host.py\
    --url "https://apps.aweirdimagination.net/camera/"\
    --receiveAudio --receiveVideo any

It will output a URL as text and QR code for the other device to connect to. With those options, the output from that device's camera will be shown on screen and the output from its microphone will be played through your speakers. That device will be sent video and audio test patterns. See ./minimal-webrtc-host.py --help for more information.

The details

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