Hi.
I’ve got trailers for most movies locally available (different formats, webm, mp4, mov). Some trailers are shown within yatse and some don’t!?
The ones showing a trailer do have trailer tags in nfo. How would I be able to get local trailers shown in yatse, too?
Yatse displays what Kodi sends 
So you need to ensure your trailers are properly recognised by Kodi during scraping.
They will auto magically appear in Yatse once Kodi is happy.
Why was I sure you answer that? 
I’ll see why kodi isn’t picking up the trailer correctly
I did sent a kodi.log snippet and a debug.log.
Added a movie (18-rc2) and kodi detects and plays well from within movie information.
Yatse’s info screen is not showing the trailer?!
Logs does not show database update, but you need to understand that what Kodi does in it’s GUI and what the API returns are 2 completely different things.
You can easily test yourself with
http://kodiip:kodiport/jsonrpc?request={%22jsonrpc%22:%222.0%22,%22method%22:%22VideoLibrary.GetMovieDetails%22,%22params%22:{%22movieid%22:51,%22properties%22:[%22trailer%22]},%22id%22:%221%22}
And replacing 51 by the id of your movie. If the field trailer is empty then Kodi does not have it and do not send it to me.
{“id”:“1”,“jsonrpc”:“2.0”,“result”:{“moviedetails”:{“label”:“13”,“movieid”:6,“trailer”:“/net/atom/media/8TB/Filme/Kino/13 (2010)/13 (2010) 720p AAC-trailer.mp4”}}}
And if you press the 3 dots button there’s no play trailer button there ?
The trailer image in the page is only youtube to play it locally.
Ah … so if there’s no trailer image, it does only mean, there’s no youtube trailer link available? The local trailer isn’t “previewed”, but is to be played with 3 dots menu?
One needs to know … ;(
Yes, 90% of users only have youtube trailer via the scrapers
For the other I have no way to play them locally and no thumb to display 
And in all cases to play them on Kodi you need to use the 3 dots menu.