Problem inserting videos in impress

Ubuntu 18.04, LO and others.
Lately inserting videos in impress has failed.
In the control program, the video displays like this

In the slide show, sound is there, but no picture.
Issue affects mp4, wmv, flv. But ogv works correctly.

Has perhaps some change to Ubuntu upset LO? If so where should I look?

My wife’s system, although nominally identical software, behaves differently. Whenever she attempts to insert a video, LO crashes.

I hope, it can help you.

Thanks ebot. I don’t think these links have told me anything new. I find codecs confusing, but I think everything is present. How can I check?

… I think …

is of some degree of uncertainty. Do your files of type mp4, wmv and .flv play without being embedded in Impress (any other application)? If not, assure it can (afaik gstreamer stuff is required)

Yes, they do. For the moment, I have worked round the problem with a shell call to vlc.