[FFmpeg-user] How to have dynamic FPS to only capture changes in i-frame

[Rocky Ji]

Hi,

I have to record lectures to preserve quality (i.e. legibility of letters)
and reduce file size, both to maximum possible extent.

In our lectures, only 2 things happen - either tutor is full screen or the
slides are fullscreen. Obviously, there is no time pattern when slides come
and when teacher comes.

Having read that some video format have I-frames that are used when scene
changes significantly, so what commands can I pass to ffmpeg to have
kind-of dynamic framerate - record only 1 frame when teacher is speaking
and then capture another frame when slide (significant change in scene)
comes or (more challenging) slide changes. It is okay to have video that
looks choppy.

I have kept audio at highest quality (untouched), but I am not sure how to
achieve the above for video part of the file.

Regards,