flicker fixer

Capturing slides sometimes has issues, and sometimes the issue is flicker. There are a few things that cause it (clock skew, network bandwidth, cpu throttling...) and going forward these will be addressed.

However, the videos created with the flicker, there isn't a practical way of fixing. (there are some impractical ways that involve too much manual work, which no one wants to do.)

I have an idea on how to fix it with some code, but it is outside my skill set to implement.
Here is my idea:

1. analyze the video: identify where the the camera and slide content is on the screen. For video produced with Voctomix, there are 5 possible compassion layouts, which seems like it would help

2. fix: look for one of the regions to be all black. If found, copy the region from the previous frame. 99% of the time it is a static image (like slides that stay up for many seconds or minutes.) and even if a transition had happened during the black, it will just happen a fraction of a second later, which is fine.

So if someone wants a nice Gstreamer or MLT project (or whatever you want to use).. have at it, I'll give it a shot.

==== update Aug 11 2024: this does a pretty good job:

ffmpeg -i in.mp4 -vf blackframe=0,metadata=select:key=lavfi.blackframe.pblack:value=20:function=less -vsync cfr -c:a copy out.mp4

https://video.stackexchange.com/questions/23589/replace-black-frames-with-previous-frames