You could also take a punt on a cheap video wall controller like this (https://www.aliexpress.com/ite...) - note there are 2 models - you would likely want the more expensive 4k one and if you want 8 monitors (7 projectors and a control screen) you would need 2 (the 3060 does a max of 4 outputs - these devices count as 1). In this case remove or disable your NVS810 as well as any iGPU and use only the 3060, run these controllers at 4k60 and the outputs at 1080p60. To blend, do everything in isadora using the stage setup.

Interesting case. Codecs etc aside, in terms of basics: what exactly are you projecting on to, how far is the audience away from the total surface, what is the nature of the content and whats happening in terms of live action in front of the projection. Of course one doesnt want stutters and stops and h264 is a red flag, just want to get a bird eye view of the situation

I’m guessing you got the NVS card to get more outputs from your system. This may not have been the best approach and a data path of cheap video wall processor with a 3090 will give better performance.

The video decoding should be hardware accelerated, but as mentioned in this thread standard sizes will decode and encode better. The number of pixels you are using is less than a 4K image, you may get good results manipulating the video so it is packed into a 4K frame and using the mapper or other actors to slice it up reconstruct it to the correct output.

Using RTX3060 graphics card as the default card for processing/calculations but the output is to an NVS810

 If I recall correctly, this hand-off between video cards is inherently inefficient and could become a bottleneck.

I don't understand first of all why the complexity of the video would make any difference since video frames are video frames. 

Well, video frames aren't all the same. You're using H264 video, which is a LONG-GOP compressed codec. Your computer has to decompress each frame of the video, which takes processing power and can slow things down and make playback stutter.
The more movement there is between I frames and P and B frames - the complexity you write about above - the more work the computer has to do. Some NVidia cards to have hardware MP4 decoding, but that would probably only be for 'standard' frame sizes like 1920 x 1080, not for 7168 x 768.

You should always use an all-I or uncompressed codec for playback in Isadora, like HAP or Quicktime ProRes.
So yes, try HAP encoding next. That should help.

HTH

Mark (not that Mark)

I'm not an expert with that but I had similar experience with just high quality Full HD videos, tried different codecs, reduce quality, etc. The freezing in my case was very random and difficult to reproduce. Finally I`m quite sure it had something to do with having the player set to Timecode instead of percentage. So I don't use the timecode feature anymore, at least during performances.

Hope this helps.