When to use bob setting in QTGMC?
 

With an 8mm source (captured with AIW9600XT) I ran it through Hybrid. Under the tabs Filtering -- (De-)Interlace/Telecine I checked the Bob box.. Guide on right side says: If enabled QTGMC will create one frame per field of the source and thus double the frame rate and count. If disabled (default) QTGMC will still create one frame per field of the source, but only output half of the frames and this keep the frame rate and count identical to the source.

When I turn on Bob (ha!) the effect is jerky motion. Going frame by frame, I can see why. It's like for every step forward in frame 1, there is a half-step back in frame 2. I guess this makes sense.

My question: in what kind of source video would one turn on Bob?

The problem you describe is incorrect assumed field order.

Avisynth by default assumes Bottom Field First for AVI input. I don't know how to do it in Hybrid off the top of my head, but the Avisynth command you need is AssumeTFF (placed before any deinterlace filter). I'm sure QTGMC also has an option to manually force either field order.

All of them.
I am not familiar with Hybrid because I prefer to manually choose all my settings rather than relying on a GUI, but when you deinterlace you want to double the framerate in QTGMC, otherwise you loos ehalf of the motion.
http://www.digitalfaq.com/forum/vide...mc-script.html

This is not true. It loses some motion, yes, but not half. Remember that QTGMC is interpolating. With some content, arguably you lose nothing. With others, noticeable motion loss (but not anywhere near as often as some seem to think).

In fact, you can create artifacts with 59.94 (50 PAL), which require more Avisynth workarounds, some of it quite complex and lengthy to encode.

So never just double the framerate, and expect it to be fine. Odds are it's not fine. Remember, deinterlace is destructive, and in every way imaginable.

My bad, but I did not understand a word. Can you give some example?

I had one in this thread: https://forum.videohelp.com/threads/...h)#post2594630

Had to get some help, poison to my rescue. :)

Ugly stuff. I started to do more 59.94/50, and started seeing more artifacts as well.
29.97/25 is safer, easier.
Plan carefully. Not blindly.

Still not clear to me what you mean.

Interlaced video:
each field contains different temporal data

When you deinterlace:
If you set QTGMC to discharge a frame:
you do loose half of the motion. If there is no motion between the different frames, you do not loose anything, but that's a special case ;)

edit: typos corrected

You're looking for frame interpolation it seems to me, check for Rife-app: https://grisk.itch.io/rife-app

This is it...