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QLab Video Switching

Let's say you have a handful of Camera or Video cues in QLab and you want to switch back and forth between them. For example, VJ-ing or live camera switching. This is deceptively difficult to do in QLab because when a cue is started, it doesn't stop the layers behind it. Usually this is a useful feature, but in this case it prevents you from going back to previously ran cues without stopping and starting them again.

 

The Quick and Dirty Fix

tell front workspace
stop active cues
start selected
end tell

Make a Script Cue with this Applescript and give it a convenient Hotkey. Pressing the Hotkey will stop all cues before starting the selected cue, preventing more than one cue from running at once and enabling simple switching. Think of it like a modified "Go," in this case it's "Stop All Then Go."

 

But what if you only want to stop and switch a few cues, like only your six camera inputs, but leave other cues running?

The Complicated Fix

tell front workspace
repeat with cur in (active cues as list)
if (((q number of cur) as number) is greater than 1000) then stop cur
end repeat
start selected
end tell

Okay, it's not THAT complicated. This will only stop cues with a Number greater than 1000. In this scenario you would number your Camera Cues 1001 through 1006 to tell the script which cues you want it to automatically stop. Now it's "Stop These Special Cues Then Go."

 

If you look closely, when you switch cues the video will hang for a few frames while the switcher cue is executed. This is because QLab has to run Applescript within the main application thread. Those still frames, however short a duration, bug the crap out of me.

In Pursuit Of Perfection

With this, the code is run in a new thread. This keeps QLab from hanging momentarily. The selected cue also starts before the previous cue is stopped, to squeeze every millisecond of delay out.

Alec SparksQLab