First on [Gopher]({{< relref "/personal/2019-06-20-gopher-maze-game.md" >}}), then in [LaTeX]({{< relref "/personal/2020-01-07-writing-a-zine-in-latex.md" >}}), it started becoming apparent that I have a predilection towards short, one-shot [Choose Your Own Adventure](https://www.cyoa.com/)-style stories on strange mediums. So in that vein, I decided to make another one, but this time played via a phone call made to a VoIP (Voice over Internet Protocol) number attached to a virtual [PBX](https://searchunifiedcommunications.techtarget.com/definition/private-branch-exchange).

To do this, I firstly needed a VoIP number. Thankfully my ISP ([iiNet](https://www.iinet.net.au/)) provides a free VoIP number to NBN customers, so that was covered. Next up I needed a virtual PBX, I went with [Asterisk](https://www.asterisk.org/get-started). This was an easy install on Ubuntu 18.04, just:

```
sudo apt install asterisk
```

Then I had to go through [setting up VoIP on Asterisk]({{< relref "/personal/2019-06-20-gopher-maze-game.md" >}}), and then I was free to start setting up the game. I had written out a little story in [Google Slides](https://docs.google.com/presentation/u/0/), using their slide linking feature to document where all the story went.

## Voice Recording

Voice recording is obviously painful, no one likes to hear their own voice played back to them. I used [Audacity](https://www.audacityteam.org/) to do the recording, because you can export to [Ogg](https://en.wikipedia.org/wiki/Ogg) easily. Make sure you record as a mono stream, then install the [SoX (sound exchange)](http://sox.sourceforge.net/) tool. On macOS with [Homebrew](https://brew.sh/) this is simply `brew install sox`.

Once you have all the recordings done and in a folder, you can convert them all to the `.sln` format required by Asterisk with the following command:

```
for a in *.ogg; do  sox "$a" -t raw -r 8000 -c 1 ${a/.ogg/.sln}; done
```

This also downsamples them to an appropriate rate. Now upload the files to the directory that contains all the Asterisk sound files, it should be something like `/usr/share/asterisk/sounds/en_US_f_Allison/`.

## Extensions Setup

The entire game is setup through extensions and contexts. So starting with your default inbound call context, add the following:

```
[inbound]
exten => XXXXXXXXXX,1,Answer()
exten => XXXXXXXXXX,n,Set(TIMEOUT(digit)=1)
exten => XXXXXXXXXX,n,BackGround(start1)
exten => XXXXXXXXXX,n,BackGround(start2)
exten => XXXXXXXXXX,n,WaitExten()

exten => 1,1,Goto(house,10,1)

exten => 2,1,Goto(forest,10,1)

exten => 3,1,Goto(river,10,1)
```

In this case, I'm using XXXXXXXXXX as a cover because my phone line is actually listed there. But what happens is we allow for a single digit press, and then play two voice files. The first says:

> You wake up in an empty, verdant field, soft grass cushioning your prone form. You stand up slowly, sluggishly.

The second goes:

> To the West is an impassable cliff. Press 1 to travel North to a house you notice in the distance. Press 2 to travel East to a dense forest. Press 3 to travel South to a rushing river that edges the field.

We then wait for the user to press a button, which leads them to the related extension. You'll notice this runs a Goto, which jumps to a different context with different extensions. You can set up the other contexts like so:

```
[river]
exten => 10,1,Set(TIMEOUT(digit)=1)
exten => 10,n,Background(river)
exten => 10,n,WaitExten()

exten => 1,1,Goto(inbound,XXXXXXXXXX,1)
```

This one plays allows for one digit to be typed, plays a sound, and then waits. If the number 1 is pressed, it takes us back to the inbound line and plays that again. You can add multiple extensions and as many contexts as you want to create as complex of a game that you'd like.

If you want to give mine a shot, try (from Australia) 08 6111 9227 or internationally I think +61 8 6111 9227 (be wary of call costs).