vMix scripts overview — vMix Master

vMix Master controls vMix from the outside, through its Web Controller. Some jobs have to happen inside vMix itself, such as making a second vMix follow the first, or lowering the program audio while an interpreter speaks. For those there are ready-to-use scripts in the vmix-scripts/ folder. They are written in VB.NET for vMix's built-in scripting.

Script	What it does	Runs on
Slave	Follows a master vMix: program, preview and playback position, by input number	Each follower
NameSlave	Follows a master vMix by input name instead of number	Each follower
PreviewNext	Puts the next input into preview after each transition	The vMix you operate
Translator	Lowers the program audio while a translator speaks	The vMix that mixes the audio
AutoGain	Keeps a microphone out of clipping and not too quiet	The vMix with the microphone
AudioFade	Fades the audio of media inputs in and out on transitions	The vMix that plays the media
DurationTimer	Writes the time left of the current input into a title	The vMix that shows the title

Which script do I need?

I want to...	Use
Make another vMix take the same program and preview as a master	Slave if the input numbers match, NameSlave if the names match
Keep a video on the follower at the same position as on the master	Slave
Always have the next input ready in preview	PreviewNext
Duck the program audio while an interpreter speaks	Translator
Stop a speaker's level from clipping or sitting too low	AutoGain
Avoid abrupt audio on clips, music and jingles	AudioFade
Show a countdown of the current clip	DurationTimer

Requirements

Scripting is a feature of the 4K and Pro editions of vMix. See vMix's own guide, Scripting and Automation, for the details of the editor.

Add a script to vMix

Open the script's .vb file from the vmix-scripts/ folder and copy all of it.
In vMix, open Settings and the Scripting tab, and create a new script. Give it a unique name, make sure the language is VB.NET, and paste the code.
Edit the settings at the top of the script, under ' ===== Configurations =====. The follower scripts also need the master's address, see Slave.
Start the script. The way vMix describes it is to create a shortcut whose function is ScriptStart and whose value is the script's name. Stopping uses ScriptStop.

vMix Master has these two functions under Scripts in the function buttons, so you can start and stop a script on the master and on every group member with one click. Type the script's name in the box next to the button.

A script can be global, working with every preset, or local, loaded only with the preset it belongs to. Tick Local Script (This Preset Only) in the editor to make it local. A script that belongs to one show, such as Slave, can be local so it only loads with that preset. If two scripts have the same name, vMix uses the first one in the list.

How the scripts behave

All of them follow the same conventions, so once you have used one the rest look familiar.

Settings are constants at the top. Times are in milliseconds unless the comment says otherwise. You edit them in the script, and they take effect the next time it starts.
They announce themselves. At start each script prints its name and version, for example 12:30:01 Slave 1.4.3, and then a short line for everything it does, such as Slave | New active: 5.
They check for updates. After starting, each script asks versions.json for the latest version and prints Update available if yours is older. This needs internet access on the vMix machine. When it fails, the script prints Could not check for updates and carries on. The vMix Scripts menu in vMix Master lists the same versions.
Errors do not stop them. A failed request or an unexpected input state is printed as Unexpected error: ... and the script tries again on the next pass.

They find inputs by name or type. Scripts that act on a particular input look for a keyword in its title:

Script	Input it uses
Translator	An input with `Translator` in the title, else the first Audio input, else the first VideoCall input
AutoGain	An input with `AutoGain` in the title, else the first Audio input, else the first VideoCall input
AudioFade	Every input with `AudioFade` in the title
DurationTimer	The title input named `DurationTimer`

Master and slave

The two follower scripts run on a vMix that should copy another one. The vMix being copied is the master, and the one running the script is the slave. The slave asks the master for its status every 300 ms and catches up.

vMix A (master) ◄─ status, every 300 ms ─ vMix B (slave)
you operate this                          runs Slave

This is separate from a group in vMix Master. In a group, every click in the web page goes to all members at once. A follower script keeps working when someone operates the master in vMix itself, from a shortcut or a control surface, without going through the page, and Slave also pulls a video back into time when it drifts. The two combine well: group the systems in the page for instant control, and run the script on the followers as the safety net.

Combining scripts

Run only one of Slave and NameSlave on a vMix. Both change the program, so they would fight.
Run PreviewNext on the master only. The followers get their preview from the master anyway.
Translator and AutoGain can share a vMix, but they pick their input by title first and then by type. Put Translator and AutoGain in the titles of their inputs so each finds the right one.

Updating a script

Copy the new version over the old one in vMix. This replaces your settings and the master's address with the defaults, so enter them again. The SCRIPT_VERSION line at the top tells you which version you have.