Hi Michael,
There are a few factors involved when it comes to post truncation. Here are some things you should know:
1. Read more tags always comes first before any truncation settings.
2. The left column of the truncation settings in Settings>Layout>Truncation contains settings for posts created using EasyBlog built-in composer, the right column contains the settings for posts created using other Joomla editors.

I found how to hide the video or image in general, but not exclusively for one post.

If you want to hide the videos and images for most posts except for certain posts, you can use the read more tag instead in those few post and insert the video/image before the read more separator. That way the image/video will show.

If you still have issues with this, perhaps you can provide us your site access so we can look into it and provide further guidance on your site.

Hi, I am not shure, if I am clear: In the listing of blog-articels every video is visible, that is embded in the full blogpost.
I need a solution to have only one media, 1 video or 1 picture or 1 cover and I need to have the choice in every post. I use not the composer editor.
Dan

PS: I solved this with workarounds for myself, but I need a "easy" solution for authors - the reason for "easy blog", isn´t it.

Hey Dan,
As I mentioned, if you want the choice of which media to show in the listings page, the authors just have to add a read more separator in blog posts. Anything above the read more separator will be displayed in the listings page. So, if you want to have 1 video for example to show, then add the read more separator after the video and before other media.

Post covers does not work with read more separators. Post covers will always display on the listings page, unless you don't have any post cover in your blog post, and it's settings will depend on the the settings in Settings>Layout>Post Cover>Post Cover Settings(Listings).