@aartwouter Hello again Aart...... we met on the VPT7 forum.
VPT7 does have a dmx in/out module available on H.C. Giljes site....... https://hcgilje.wordpress.com/vpt/ but you need an Enttec Pro dmx interface. True, it's not artnet. Maybe that would help, but if you are still having trouble with your video then maybe it will not? Have you already tried a native .mov movie file?
You could try TouchDesigner for a ready made solution. It does most video stuff (quite powerful), and has a chop module "dmx in" which can receive from artnet devices. For non-commercial use it is free....... http://www.derivative.ca/
If you have ever used "Blender" you will understand it quickly.
Pure data is fairly similar to Max, which VPT7 was built on, and there are some very extensive patches already developed for video here......... https://puredata.info/downloads/extended-view-toolkit That toolkit also contains an ArtNet sender that is built with standard Pd objects, so reverse engineering a receiver would be fairly trivial.
As you will see at the top of that page, you will need and older version of Pure Data for it to run well........ You will need a 32-bit version of Pd.....
((extended-view-toolkit needs 32bit Pd and Gem for what you need, and nearly works (much of it does) with http://puredata.info/downloads/pd-extended .......BUT it was built for Pd Vanilla, and tested against Pd 0.43 vanilla with Gem added in. Adding Gem in can obviously be done, I will look for a link))
The video capabilities of Pure Data with Gem are being forgotten at the moment as Pure Data goes over to 64bit (Gem is only reliably available in 32bit). Gem uses OpenGl as does VPT7.
You might find the learning curve a bit steep with Pure Data. I would definitely look at TouchDesigner and see if it will do what you need, although if you need to buy a commercial license it is not very cheap.
If you decide to upload your video (or a partial chunk of it) and a copy of your VPT7 folder with the effects set I will try it on my machines and see if I am having the same problems as you. I have an Enttec DMX Pro somewhere as well. Upload it to a real transfer site though...... it would probably put this forum out of action for a day or two. Open a chat with me on this forum to send me the link.