Question: As mentioned in the title, I'm unable to simultaneously record my headset microphone *and* my desktop audio when using SimpleScreenRecorder in KDE Neon 5.24.

In the "Audio Input" section of the recording settings, I selected "PulseAudio" as **Backend**, whereas for **Source** I've tried both "Built-in Audio Analog Stereo" as well as "Monitor of Built-in Audio Analog Stereo" (see below):

[![enter image description here](https://i.stack.imgur.com/Iagkh.png)](https://i.stack.imgur.com/Iagkh.png)

When selecting "Built-in Audio Analog Stereo", the microphone gets recorded but the desktop audio does not, while the situation is exactly the opposite when I select "Monitor of Built-in Audio Analog Stereo" (can record desktop audio but not headset microphone).

Does anybody have an idea of how to solve this issue?

Answer: 
With the [standard `paste` command](https://pubs.opengroup.org/onlinepubs/9699919799/utilities/paste.html):

```
$ paste -sd ',,\n\0' file
St1,number1,1234
St2,number2,456

```

`s`erially `paste`s the lines of `file` with `,`, `,`, *newline*, *nothing* (not a NUL character as one might think) as `d`elimiters in turn.

Or:

```
$ paste -d ',,\0' - - - - < file
St1,number1,1234
St2,number2,456

```

`paste`s stdin 4 times with `,`, `,` and *nothing* as `d`elimiters between them.
Try `awk`:

```
awk '$1=$1' OFS=, RS= file
St1,number1,1234
St2,number2,456

```

The empty record separator `RS` targets the "blank line", and assigning a field (here: `$1`) makes `awk` reassemble the entire record from the fields using `OFS`.
It assumes `$1` never being 0 or NULL/empty.