Audacity can record computer audio (including sound from YouTube, Spotify and more).
Video tutorial for Windows
1. Select the loopback device
Click on Audio Setup and select Windows WASAPI as the Host.
Select Windows WASAPI in Audio Setup > Host
Select the output you want to use (the device you're using to listen) as the input. It will be marked with a (loopback) after it's name.
Select the loopback option for the device you want to record audio from.
When using the (default) MME device, you may find a virtual microphone called Stereo Mix, What you hear or similar in it. This also will record your desktop audio.
Selecting Stereo Mix as an alternative to record desktop audio
Note: MacOS does not have built-in desktop audio recording capabilities. You'll need to download Soundflower to record desktop audio.
Soundflower
Caution: Soundflower is not compatible with Apple Silicon-based machines ("M1", "M2", ...)
Open the Audio MIDI Setup app (found in /Applications/Utilities).
Press the + button in the bottom left corner and select "Create Multi-Output Device".
In the panel that appears to the right, select Built-in Output and Soundflower (2ch).
Press the gear button in the bottom left and select "use this device for sound output".
Note: If you don't set an option, you won't hear anything after completing the following steps.
Start Audacity
Click the Audio Setup button and set Soundflower (2ch) as the recording device.
When using PulseAudio (default for Ubuntu, Linux Mint, and others):
Install PulseAudio Volume Control (pavucontrol). This should be in your repository already.
Use the Audio Setup toolbar to select ALSA as the audio host and select pulse as the recording device.
If your system uses Pulse by default, the pulse device may be called default.
Enable the recording meter by selecting Start Monitoring.
Click the Microphone icon to start monitoring the recording level
Open PulseAudio Volume Control and choose the Recording tab.
In the Capture from dropdown, select the "Monitor" option of the playback device used by the application you want to record from
PulseAudio Volume Control - Select Capture from: Monitor of device
Launch the application that you wish to record and begin playback.
In the "Recording" tab of PulseAudio Volume Control, drag the volume sliders so that the recording level in Audacity's Recording Meter is to left of 0 dB (-6 dB is a good level to aim for).
2. Check if everything is set up correctly
Recording the desktop audio will record all desktop audio, including notification-pings, games, and Audacity itself (for example, other tracks in the timeline if you're using overdub). So unless you specifically want these noises, make sure to turn them off.
DON'T use software playthrough when recording desktop audio. Make sure it's off in the menu: Transport > Transport Options > Software playthrough (on/off) - The ✔️checkmark next to it must be turned off. You can turn off overdub here as well.
3. Record
Hit play to ensure audio is playing and then the record button to record your desktop audio.
Ensure audio is playing first when recording desktop audio as although WASAPI can record a silent audio stream it can’t record when there’s no audio stream.
