Problems with VDMX unable to handle alpha layers?


I’m having a confusing problem with alpha layers that happens in VDMX, but is not a problem in other apps. I don’t know if my setup is wrong or VDMX handles this in a peculiar way I can’t figure out.

See these three still examples, they are all created with exactly the same files (linked) layered a top each other: A Scene-Background, then Artist Insertion and then a Scene-Front-Overlay, where the Overlay has a prepared alpha channel that masks out the desired frontal elements. (The Artist Insertion layer / idea can be removed, the problem persits, that layer is only included to visualize my goal in case that helps figure out another route.)

First Motion, then VDMX:


In VDMX, the clouds are coming out all wrong, they should simply just be half transparent. The mask borders are visible.

Again clouds wrong, they should be half transparent, and again another problem with the mask border, kind of inverting over the ridge to the right.

The straws, the person moving mask, its just all really messy in VDMX, but not in Motion. These examples are also much, much, much worse in video than in stills, because the “illusion” breaks down as the layers become obvious. The dropbox below can demonstrate the problem better.

Why can’t I layer these fronts similarly in VDMX to other apps? I have tried ProRes 422/4444, HAP/A, HAPQ/A, I’ve tried the layer modes Over, Mix, VVSourceAtop, and even did a version where I replaced the alpha with a green matte to then further key it out on the front layer, the result was the very similar, its like the masking trick is PUNCHED FRONT and I cannot understand whats happening. I thought it perhaps was due to microscopic timing, that the layers are off by a frame or CPU slice or whatever that is, but freezing the images (pausing playback) and setting the exact same frames on top of each other makes no difference, problem still stays. Perhaps this is impossible? But that is equally perplexing, this is such a basic trick, I can’t believe VDMX can’t do this. Motion and FCPX has zero problems layering these files, the overlay works perfect there, the matte is invisible.

You can verify and try this out for yourself, here is a dropbox with the files (ProRes 422/4444 - you can transcode to HAP variants, for me the problem is the same in all codecs) and a simple VDMX project to trigger them (naturally both Background and Front needs to be triggered simultaneously, keyboard shortcuts 1-2-3 helps with this). You can drag the files into Motion and FCPX and verify for yourself that the mask completely disappears in those apps when they start simultaneously, Motion project attached to demo.

Note: The masks ARE shitty when seen standalone, but that isn’t a problem when they are placed on top of their own source, the rough shittiness disappears, in all other apps. It’s not perfect in Motion either, but for a live stage production with fast cutting (these are a few of hundreds of cuts), the Motion and FCPX versions passes, the VDMX does NOT…

Very happy for advice, of course if a simple blend mode formula would fix this i’d be psyched but I fear I have to rethink (or re-app) this?



My guess: Motion is doing some kind of spill suppression.



Looking at your content I think you have a sync issue with the foreground and background layers. You need to set up the play button to start both layers at the same time. On both layers attach a keyboard key to the play button (/key/1) and add a marker at 0 (/key/2). That way you can stop/start and reset to 0. This will help keep the layers in sync.

Remember each VDMX layer is independent with its own timeline where as in FCP or Motion you have a single timeline. VDMX layers can have all sorts of time speeds and jumps attached to them, it’s a very different environment from a regular video editor.

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Thank you guys! Did you try that with the attached files on your end, does that work for you on your end? It doesn’t for me, I also thought it was sync related at first! But the attached dropbox project does what you suggest; layers are triggered simultaneously with the same keys. If you take a look at the attached project, it’s triggering like you advice. And as I wrote in the first post, to check specifically for this problem, I stop playback and manually align same frames atop each other. The problem persists, just frozen.

I can force the potential consequence of this issue on its own by nudging the front layer one frame or more ahead - then I see a related but different problem (the mask edge is then super obvious and there is a “doubleness” feeling to the image). This leads me to believe that the layers are actually enough in sync, it is not a drift issue.

In the full performance project drift IS a problem in itself, the main set is much more complex than this problem-demo, the machine is pushed to the limits and then granted every now and then the different layers do slide in and out of time and sync and masks borders are subtly affected now and then. I can live with that, It is not enough to be a huge problem.