I have been recently experiencing an issue with Light Flicker in Drangonframe 4, but the strange thing is that it is only happening in High Res mode. I use a Canon T5 as my camera. All my settings are set to manual. I also have manual focus on and auto stabilization off. There is no outside light coming in, and I am wearing dark clothes in order to avoid flicker from my clothes. There are also no lights behind me that could be causing the light flicker. The only thing I can think of is that it has to do with either the software or my lens/camera.
Below is an example of the issue I am facing. It is a clip that has been exported in High res mode. I want to note again that this issue does not occur when exporting/viewing my project in the low res mode:
I have attached the same file but exported in low res mode as well.
It looks like an overall light change, which can be from the camera or from the mains power supply fluctuating by a small amount, so all the lights actually do get a tiny bit brighter and dimmer over time. Not like shadows or reflections from you moving about. But when I got flicker from lights changing, it was not as continuous. I would get several frames the same (shot over 10 or 20 minutes) then a shift, then another shift after a few more frames. My multimeter in front of the camera and hooked up to mains power showed a gradual shift in voltage of 1 volt or less, and the frames with the needle higher were the brighter ones. So the camera was doing a good job of recording that. It is possible that the video assist does not register such small changes in brightness, but the hi res image does. I have a power conditioner to smooth out the voltage now, it drops a couple of volts but output stays steady.
Are you using a Canon lens, with the aperture controlled by the camera body? Normal operation for a still camera is for the lens to open up between shots to give you a nice bright view. Then it stops down to where you set it, as you press the shutter, but does not always stop down to the exact setting. I use a Nikon manual lens with adapter, so the lens stays stopped down to my setting - f-11, f-16 or whatever - all the time, and does not vary.
Another possible cause of this kind of rapid flicker is using fluorescent lights, which actually do flicker very rapidly. One frame might get the fluoro at full brightness, one at minimum brightness, one half-way. (I got a similar rapid flicker effect with my 16mm Bolex when shooting high speed 48 fps, and left fluoro room lights on to boost overall brightness to make up for the shorter exposure time. Unusable, had to borrow more halogen lights and re-shoot.) For stop motion I use long exposures, usually around 1 sec to 2 sec, which averages them out, so the flicker is gone if I do have any fluoros going. With smaller f-stops the live view gets very dark, because the video does not benefit from the longer exposure, so I have to adjust it in the Cinematography window, usually to the maximum gain of plus 4, to see what I am doing. It usually looks a bit noisier than your video assist footage, so I am guessing you are not using as much gain to brighten it. I might expect the video assist to also show some flicker though, since it has to be a short exposure, since it needs to fit into the frame rate, but video is less sensitive to very small variations.
If none of your lights are fluoros then that won't be it. I know that when I first used my Canon 7d there were a few more settings in the menus I had to turn off, like edge compensation, that were not in my 40d, and were making helpful little adjustments and giving me flicker. I had to go through every single menu. I don't know what the T5 has, but there might still be a sneaky setting somewhere.
I got smoother power in the night time, when local factories weren't turning their machinery on or off, but who wants to animate in the graveyard shift all the time? I could also induce the voltage drops for testing, by turning my oven on and off, and seeing the meter react and the light change - but light dimming not visible to the human eye in real time, only with frames taken one at a time.