When using Gwenview to show photos with videos included, it gives the sound with a black screen. On advancing to the next image it give the message "qwenview requires an additional plugin to decode this file. The following plugin is requried: XVID MPEG-4 decoder. Do you want to search for this now?" If it searches for this it fails. Previous versions of Gwenview played mp4 videos. The 4.12.3 version does not, but it will play .MOV files!
Created attachment 85633 [details] Example of Gwenview's response to a mp4 movie As I have not had any acknowledgement of this problem, I thought I would show an example of the problem. This shows the black screen present for the full duration of the movie followed by the message from Gwenview which is always unsuccessful at finding the required package. Previously Gwenview would play jpg files and movies in the correct order, unlike what MS Windows packages do. If you cannot replicate this problem, please let me know.
I have finally got Gwenview to show mp4 files by installing the package "phonon-backend-vlc". So it looks as though this package should be added as a dependency for Gwenview.
I had the same problem after upgrading to Kubuntu 14.04. Gwenview showed all the colours wrong in mp4 videos. Adding the package "phonon-backend-vlc" fixed it. Thankyou Samuel for finding the fix.