www.makemkv.com

New to MKV but had used ISO. How to I get MakeMKV to not copy the trailer previews?

Don't select them for ripping. Or you can set the minimum title length in preferences to be greater than a typical trailer length. The default is to ignore stuff less than 120 seconds long.

Ok, so how do you tell which they are?

Are you trying to do a "backup", or ripping to MKV files?

Ripping to MKV, you will be presented with that are at least as long as your minimum title length, and you can select them. Ones shorter than your feature length are almost certain to be "extras", while "previews" are generally 1-2 minutes in length.

Not knowing what disks you're ripping, I cannot tell you which ones are which.

My method is to rip everything over 30 seconds in length, then play them with VLC. If it isn't something I want to keep, it gets deleted.

If you're trying to do backups, MakeMKV is going to save EVERYTHING. Otherwise, it wouldn't be a "backup".

I did some more experiments and found still having issue with previews. First, it is set to exclude anything under 120. I just did a disk and only selected the main title. Yet when I play the file, it starts out with a 1 min 5 second movie preview. And it kept the Universal 10 second earth shot. Any suggestions? I don’t remember thus being an issue back in the days of ripping you ISO and XBMC.

I don't think I've ever ripped a movie that had the preview baked into the main feature. What movie are you trying to rip?
As to the movie studio opening, that's part of the movie. If you really need to get rid of it (and for some movies that would mess up the sound) you could use MKVToolNix.

Croogs a new age

Now this is just crazy. I just tried to play it from my iPad and no trailer preview but twice last night when I played it from the Apple TV 4K 2021 it did a trailer preview and of the same movie. This is using Plex.

Are you certain that's not a "feature" of Plex? Emby has a function called "Cinema mode", which does what you describe... play 1-2 "random" trailers prior to starting the main feature. It can be disabled (per client), but could easily be mistaken for being part of the video.