gstreamer tips and tricks

18 Mar 2020

Tags: gstreamer linux command-line

Streaming video from internet to /dev/video0

For cases where you want to use your desktop to do face-to-face meetings with others but don’t want to go out and buy a webcam, this is for you.

Prerequisites:

To start, install an app on your phone that streams video from the phone’s IP address (for Android users, there is IP Webcam). Start the server up. Pay attention to the URL that streams raw video (for IP Webcam, it is /video).

To activate the v4l2loopback kernel module, run the following command:

sudo modprobe v4l2loopback

You may notice that it automatically creates a new loopback device (usually /dev/video0 if you don’t have other webcams plugged in).

Run gstreamer:

gst-launch-0.10 souphttpsrc location="http://<URL>/video" is-live=true !
	multidec ! decodebin ! v4l2sink device=/dev/video0

Note: You can replace the video URL with any video you like and have that video stream into /dev/video0.

Streaming audio from internet to computer

For cases where you don’t just want video from your phone, but audio as well, this is for you.

Prerequisites:

This time you don’t need to use v4l2loopback since we are streaming the audio directly to our device. You will be able to hear the audio in your headphones.

After setting up the server for your phone, pay attention to the URL for the audio streams (there are 2/3 for IP Webcam: /audio.wav, /audio.opus, /audio.aac, depending on if your device supports them; we will use /audio.wav).

Run gstreamer:

gst-launch-0.10 souphttpsrc location="http://<URL>/audio.wav" is-live=true !
	decodebin ! autoaudiosink

Streaming audio from PulseAudio device to computer

For the cases where everyone tells you to use meet.google.com for meetings and you have a USB microphone and want to join but for some reason Google doesn’t recognize your USB microphone but for some other reason recognizes the sounds your device makes (system monitor) even though other sites that test microphone have no trouble recognizing both the system monitor and the USB microphone at the same time.

Prerequisites:

Plug in your microphone. We have to find the device’s name. Run the command:

pactl list | grep -A2 'Source #' | grep 'Name: ' | cut -d" " -f2

You will see a couple of devices listed. Pick the one you think is correct. Usually the correct one is prefixed with alsa_input.

alsa_input.usb-BLUE_MICROPHONE_Blue_Snowball_SUGA_2019_11_14_29386-00.mono-fallback
alsa_output.pci-0000_00_1b.0.analog-stereo.monitor

Copy the entire string and run the following command:

gst-launch-0.10 pulsesrc device="<YOUR DEVICE NAME HERE>" ! autoaudiosink