Flickering video effect automation.

[Leon Cox]

I'm tying to automate a video effect of a, Gamma value on a video file, to add some flicker to approximate an old-timey projector.  Think silent film era type.  The video is stills with some page turns baked in like turning pages in a comic book.

The video file plays and pauses multiple times and I need the "flicker" to persist through all the pauses.  

Ideally I'd like to have a fade on the Gamma parameter between say 1 and 1.3 oscillate say 12 to 24 times per second.  

My musical brain says to get an LFO going and MIDI/OSC into the parameter.  The "Video FX Gamma" would work great for this.  I don't see any Video FX with any sort of time or rate options. 

I've tried mapping a fade to the parameter but having one fade repeat that fast really messing with QLab and the video starts to slow and throws off all the timing. 

I will try a custom fade cue with lots of up and down values next.  Although I haven't had much luck grouping and looping a fade cue.  Adding a Group seems to only allow audio cues and I'm wondering if I have some sort or error happening in 5.2.4.  But, I digress.

I expect a set of OSC commands or a Script that changes the Gamma value could accomplish this but I am woefully ignorant of how to achieve that.  But would like to learn. 

Can one put timings into scripts?

Am I just missing some sort of filter/Video FX that's hiding in a menu?

Thanks all, first time nerding with y'all.

[micpool]

The wiggly fade method is the best way to do this, but you will need 2 fades e.g .9-1.5 and 1.5-.9 so you can loop them



Put a 0.01 pre wait on the group to ensure the start cue starts again each time the group is looped.

Screen recording and workspace attached. Replace the missing media with your image.

Mic

[Leon Cox]

First things first.  The "adding a Group seems to only allow audio cues" was a glitch.  I was using the drop down menu to add a group and it was at the top of the menu.  After a reload it moved to the 10th item in the menu, the first being "Audio".  So this is why trying to add a group was adding an audio cue.  The same thing happened today.  The menu was reordered and even "Command 0" still added an Audio cue and not a Group so it's not just a temporary order of the menu thing.  It seems to be that once I add a cue it returns to the intended operation.  ie. hitting "Command 0" twice in a row added an Audio cue first and then a Group cue.  I'm sure this has been fixed in updates as I'm on 5.2.4 currently.

Back to the meat of the matter.

I have an acceptable result by creating a custom fade to automate the Gamma value.  I saw an example someone had used to make flickering light to create a fire effect.  When I had originally tried to loop a couple of very fast fades it caused playback issues and sometimes erratic behaviour of the the timeline; specifically, missed pause cues for that same effected video.  With this new custom fade I simply added multiple up and down points creating a sawtooth.  I needed 2 because 1 would leave the value in a place where repeating it would no longer cause any effect on the next pass.  Fade out on effects parameters doesn't seem to be a thing (how to I do it without stopping???.  Again, I'm pretty new so please don't attack my ignorance :) ) (Thanks member:micpool for adding that as the first response, in the middle of this book I'm writing.  I've only been here a day but I understand you are a mighty contributor and I thank you for your help) 

So, this worked great to produce the effect I wanted..... BUT..... I wanted the video to fade in from black with the effect fading in with it; like a projector lamp warming up, not like a shutter opening.  Fading in the fade, also doesn't seem to be a thing.  It would need to be applied as a relative thing and that doesn't seem to be a thing either.  I'm not sure how to "math" that either but, I digress.  So, the result would be that I couldn't fade in the effect of the flicker with the video fading in. Starting the flicker ahead of time, with the video opacity at zero, and then fading in the video would cause it to jump to full opacity during the fade and the effect would be way more dramatic until the opacity fade was complete, then the effect would look as intended.  I never did find a way to sort this out.  I was confused as the fade in was affecting opacity and the effect fade was affecting gamma.  

Again, I went back to trying to find a stand alone LFO to work on the Gamma value via MIDI, or to write a script (huge learning curve for me, how does one incorporate timing into a script). 

Then the same problem happened with the fade out.  If I stopped the effect fade first, then the video fade would work as normal.  If I tried to fade the video and the "flicker group" together, then the video would snap out.  I wanted the video to fade out as if the flicker was baked in (it could not be because at this point, and various other points in the previous 5 minutes, the video was paused).  There was a lot of complicated head scratching and then the simplest of solutions hit me. ... JUST COVER IT ALL WITH A BLACK PICTURE!

So, because this whole set of cues, involving this "flickering video", comes from black, I start the stack with a black picture placed on top of the video element.  The video is started and paused, to the first freeze before any motion is temporarily needed, and the video flicker stack loop is started (just like micpool's example below), and then my first cue is now fading out the black cover picture instead of fading in the video.   At the end I fade the black picture in over top of the video before stopping the flicker effect and video.  

This produces the results needed and I didn't have to learn any scripting or install anything new or interesting on a client show laptop.  It also saved me from putting a fan on a lighting dimmer in front of the projector lens :)

Now the whole video cue looks just like the archival footage that was sent to me.  Too bad the only reason it looks like that wasn't a design choice but an artifact of the framerate difference between their projector and video camera.  (the dang intermission slide flickers too) 

I hope this has been a worthwhile addition to this group and I'm looking forward to digging around looking for other cool things to do with Qlab.  

[micpool]

On Monday, February 5, 2024 at 5:41:48 PM UTC coxfreelan...@gmail.com wrote:

Then the same problem happened with the fade out.  If I stopped the effect fade first, then the video fade would work as normal.  If I tried to fade the video and the "flicker group" together, then the video would snap out.  I wanted the video to fade out as if the flicker was baked in (it could not be because at this point, and various other points in the previous 5 minutes, the video was paused).  There was a lot of complicated head scratching and then the simplest of solutions hit me. ... JUST COVER IT ALL WITH A BLACK PICTURE!

Fading a black still over the top of another image is a good way of fading things in and out, particularly if you have stacked images in a group.

It is not neccesary in this case because it's perfectly possible to fade an image in and out independently of  it's gamma being  faded in and out by other fade cues.

In each fade cue you can select which parameters the fade cue acts on.

So in this screenshot the cues that fade the image in and out act only on the opacity of the target (all the fades target the image)  while the cues in the looping timeline group only act on  the FX  Gamma value

Workspace attached replace missomg image with your own

Mic

[Leon Cox]

For me, this didn't work.  With my "Flicker Group" active (affecting Gamma of a "Video FX"), I then faded in the opacity of my video.  While this was happening the observed affect was that the video would strobe violently until the video fade was complete.  Then the Gamma fade "Flicker Group" would affect "effect" the video as intended with a much less intense Gamma flicker. 

[micpool]

Try with the workspace I attached to my last post and see what happens.

Screen recording attached

[Leon Cox]

Thanks, I will.  I'll try to regress my session and post it if it's repeatable.  Currently in rehearsal with it. 

[Leon Cox]

I tried a test pattern in your workspace and it worked great.  I replaced the test pattern with my show video and it also worked great.  (first time it crashed Qlab pretty hard) 

I tried recreating (not from scratch) what you'd done in my older file and it did the same full intensity strobe.  

Sooooo, I've missed something and with a little digging I think I'd copied the fade cue and it had retained the Opacity check box.  Now my erratic behaviour makes sense.  It was doing exactly what it was supposed to.  Both of my flicker fades had Opacity 100% checked so after the first one completed it stayed at 100% for the rest of the loop as the second fade cue also having an Opacity of 100% would then be fading from the current state of 100% to 100% hence no change after the first fade in was complete. T'was a long day ;)

Now I can clean my file up a bit as ordering things got a little ugly to work around my error.  

Thanks again micpool, it really should have been as easy as I'd thought in the beginning.