Slave

Slave makes a vMix follow another one, the master. When the master puts an input on program, the slave takes the same input to program. Its preview matches the master's, and when both are playing the same video, the slave pulls its playback back into time if it drifts.

Use it for multi-language streams, a hot backup, or several rooms that need the same program, as long as the inputs have the same numbers on every system. If they are named alike but numbered differently, use NameSlave.

Requirements

• Input N on the slave is the matching input of input N on the master.
• The slave machine can reach the master's Web Controller, for example http://192.168.1.20:8088/api.
• The transition set in TRANSITION is available on the slave. The default is Stinger1.

Set up

1. Add the script to the slave vMix, see adding a script.

2. Set masterAPI at the top to the master's API address:

   Dim masterAPI As String = "http://192.168.1.20:8088/api"
   

   While it still has the placeholder http://192.168.x.x:8088/api, the script prints Please update the masterAPI ... Exiting... and stops.

3. Change the settings below if you need to, and start the script.

Settings

How it works

Every LOOP_TIME the script reads its own vMix and the master's status, and then compares three things in order.

1. Program. If the master's active input differs from the slave's, the slave runs TRANSITION with the master's input number and waits TRANSITION_BUFFER.

2. Preview. If the master's preview differs, the slave sends PreviewInput with the master's preview.

3. Playback position. The position is corrected only when all of these hold:

   • both are on the same program input,
   • the master's position is not zero,
   • the difference is bigger than POSITION_THRESHOLD,
   • the master is Running,
   • the slave's copy of the input is longer than the master's position.

   The slave then sets the input to the master's position, starts it with Play if it was not running, and waits TRANSITION_BUFFER.

Good to know

• Position sync is about not letting two machines drift apart by minutes, not about frame accuracy. With the default threshold, a difference of up to 30 seconds is left alone, because every correction is a visible jump. Lower POSITION_THRESHOLD for a tighter match.
• A paused master is not followed. The position is only corrected while the master runs.
• If the master cannot be reached, the request times out after five seconds, the script prints an error, and it tries again on the next pass.
• In vMix Master you can group the master and the slaves so clicks reach all of them at once. The script then acts as the safety net that keeps them together when the master is operated from vMix itself.

Log messages

• Slave | New active: 5: the slave took input 5 to program.
• Slave | New preview: 9: the slave put input 9 in preview.
• Slave | Position sync: 00:02:10 (diff: 41s, state: Paused): the slave jumped to 2:10. The difference and the state are the ones from before the correction.
• Slave | Unexpected error: ...: a request or an input read failed, and the script retries.

Troubleshooting

• Nothing happens. Check that the script is started, that masterAPI is correct, and that you can open the master's API address in a browser on the slave machine.
• The wrong input is taken. The numbering differs between the systems. Fix the numbering, or use NameSlave.
• The program does not change. vMix may not run TRANSITION if it is not set up on the slave. Try "Cut" or "Fade" to check.
• A video keeps jumping. The two systems have different files behind the same input number, so the positions do not line up. A slave whose input is shorter than the master's position is skipped on purpose.