Show Control Broadcast

Show control broadcast is QLab’s name for a set of MIDI Show Control (MSC) and Open Sound Control (OSC) messages which report on the status of a workspace while in performance. These messages can be used to monitor QLab’s status, for example by a stage manager or director of production who wants to be kept informed about “where we are” in the show, or used to remote-control another device by having that device start cues of its own whenever a matching cue in QLab starts.

Show control broadcast can be switched on and off per workspace, and is entirely optional.

Show Control Broadcast With MSC

MSC show control broadcast uses the same MIDI output patches that MIDI cues and MIDI File cues use. To configure MIDI output patches, visit Workspace Settings → MIDI → MIDI Outputs.

Once you have at least one MIDI output patch configured, go to the MSC Broadcast tab.

The MSC Broadcast tab

The upper left corner has a checkbox which allows you to enable or disable MSC broadcast messages for the entire workspace. To add an MSC broadcast output, click on the New Destination button or use the keyboard shortcut ⌘N while this tab of this window has focus.

Each destination is an individually configurable output for MSC broadcast messages, which requires three settings:

  • A MIDI Patch, which the MIDI output patch that will receive the messages. The MIDI output patch, in turn, connects the workspace to a MIDI device (or virtual device, such as an IAC bus or RTP-MIDI session.)
  • Under the Message heading is a pop-up menu which lets you set the command format for the destination. Command format is an MSC term for the category of device or software that will be receiving the messages. The MSC spec defines a number of specific categories and each device or software must self-identify as belonging to one or more category. QLab itself, for example, responds to messages in the Sound (General), Video (General), and Lighting (General) categories. Refer to the documentation of the device that you’re sending messages to in order to learn which category to use.
  • Also under the Message heading is a field to enter the Device ID of the device that will be receiving the messages. Device ID 127 is the “all-call” ID, so if you set a destination to use, say, the Lighting (General) format and device ID 127, then all devices which are physically connected to that MIDI output patch and which self-identify as Lighting (General) will receive the messages.

To remove a destination, click the button at the right edge of that destination in the list.


In the screen shot above, there are three MSC broadcast destinations.

The first one sends MSC messages to “All Types” via an IAC bus. Since IAC busses are internal to the Mac, any other programs running on the same Mac which are using device ID 9 will receive these messages.

The second one sends MSC messages to “Lasers” via a different IAC bus. Any laser-specific software running on the same Mac which uses device ID 2 will receive these messages.

The third one sends MSC messages to “Robots” via an RTP-MIDI session. Any robots out there listening to the same RTP-MIDI session and using device ID 53 will receive these messages.

MSC Show Control Messages

Action in QLab Corresponding MSC message
GO MSC GO {cue number of the cue which ran}
HardStop All MSC ALL_OFF

Show Control Broadcast With OSC

OSC show control broadcast consists of a set of OSC messages which another program or device can send to QLab which will cause QLab to keep that other program or device informed about show control status. If the QLab workspace is closed and reopened, the remote program or device will need to re-send the message to continue receiving updates.

Messages To QLab

The highest-level commands are /listen and /ignore which start and stop the flow of all show control messages.

Message sent to QLab Result
/listen Client will receive all show control messages.
/ignore Client will stop receiving all show control message.

Once a client requests updates, QLab can send show control messages in three basic forms.

Workspace Event messages with arguments

The first form of OSC show control broadcast message is a workspace event message with arguments, which looks like this:

/qlab/event/workspace/{event} {cue number} {cue name} {cue uniqueID} {cue type}

Action in QLab Corresponding {event}
GO go
Audition Go auditionGo
Stop cue/stop
Start cue/start
Playhead move playhead

When any of those events occur in the workspace, the corresponding message will be sent with arguments filled in based on the cue that was related to the event. For example, consider this screen shot:

OSC broadcast example

If someone pressed at this moment, QLab would send this show control broadcast message:

/qlab/event/workspace/go "24" "intro music" "F8CD48F4-B06B-4992-ACD6-5753D0224" "Audio"

QLab also sends four individual messages containing each of those four arguments individually:

  • /qlab/event/workspace/go/number 24
  • /qlab/event/workspace/go/name "intro music"
  • /qlab/event/workspace/go/uniqueID F8CD48F4-B06B-4992-ACD6-5753D0224
  • /qlab/event/workspace/go/type Audio

GO and Start

Whenever a cue starts for a reason other than a , that is considered a “start.” So, if cue 1 is a Start cue which targets cue 2, and you select cue 1 and press , QLab would report a /qlab/event/workspace/go message for cue 1, and a /qlab/event/workspace/cue/start message for cue 2.

As far as show control broadcast is concerned, “previewing” a cue is the same as “starting” it.


Whenever a cue stops, whether it’s stopped manually or as a result of a Stop cue or because it simply runs out, QLab reports a /qlab/event/workspace/cue/stop message for that cue.

Playhead Move

Whenever the playhead in the current cue list wrap moves for any reason, QLab reports a /qlab/event/workspace/playhead message for the cue that the playhead moves to.

Workspace Event messages without arguments

The second form of OSC show control broadcast message is a workspace event message without arguments, which looks like this:


Action in QLab Corresponding {event}
Pause All pauseAll
Resume All resumeAll
Panic All panicAll
Stop All stopAll
HardStop All hardStopAll
Reset All resetAll

Whenever any of those events occurs in the workspace, the corresponding message is sent.

Setting scope

While a comprehensive set of show control messages is hardly overwhelming, it still may be desirable to receive only a subset of these messages instead of every single one.

To that end, the /listen and /ignore messages have a set of extended forms which allow you to receive or stop receiving exactly the show control messages you want. The extended forms look like this:

/{command}/{event}/{optional detail}

  • {command} can be either listen or ignore
  • {event} can be any event listed above, such as go, playhead, cue/start, or stopAll.

You can stop there with messages like /listen/go or /listen/resumeAll, or add any of the following optional details:

  • number
  • name
  • uniqueID
  • type

Adding those details further reduces the variety of messages which get sent.


If a client sends QLab only this message:


It will only receive /qlab/event/workspace/go messages, including all forms of that message with all arguments.

If a client sends QLab only these messages:

/listen/go/number, /listen/panicAll

It will receive one /qlab/event/workspace/go {number} message with every with only that single argument. It will also receive a /qlab/event/workspace/panicAll message whenever the workspace panics.

By using the extended forms of /listen and /ignore messages in combination, you can subscribe to the exact set of messages you want, with nothing extraneous.

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