I want to run Video while a song is playing in ST3...

Sure you can send MIDI. See here for details: https://stagetraxx.com/user-guide/midi/

Without posting details about your setup, there is not much more to tell at this point.

GtrGeorge Something has to create or host the content for the projector to project. The projector is simply a sort of TV screen. It show whatever something tells it to show.

Try looking at something like Vivibox. Its software that hosts video that can be played from the HDMI output of a laptop. The HDMI cable is then connected to the projector.

Yes Stage Traxx can send the commands (MIDI) to switch to the right song and then start the file playing.

I use an Arduino Leonardo with a midi shield to receive midi and depending on what it receives/I send uses the keyboard.h library to send key strings to my PC as a usb keyboard input. You can even use it to input mouse controls.

I use a simple PowerPoint presentation with videos and/or graphics on a black background. To select a slide in PP you just need to press the slide number and enter.

I use it by sending a reading a note and velocity and assigning each velocity number to an ascii character. I use note 0. So if I send [midi: N0.49@6, N0.10@6] to my board which I have assigned as device no 6 then it will send an ascii number 1 followed by a line feed to the PC. Were you to send a B then the screen would blackout or send a W to whiteout the screen.

Alternately I could on the Arduino program a PC to output a full complex string of commands to both keyboard and mouse with all of its needed timings triggered by a simple midi PC on ST3.

Bit complex if you don’t use Arduino but worth learning as it is so adaptable and very inexpensive.

To give an example I use it when I sing a song by Matt Monro called “on days like these” from the Italian Job while I show a video of a Lamborghini driving through the Alps in a similar way to the opening credit of the film all triggered from a couple of midi commands from my ST3