Our 3.2 Omeka installation does not create thumbnails from pdf and mps files that we add, whereas re-creating derivatives from jpeg formats works as intended.
The Derivative Images plugin only re-creates thumbnails for files: it’s intended to be used when you’ve changed your settings or something like that and want to add or update thumbnails for files that are already uploaded.
It just uses the regular thumbnail generation process that gets used when you first upload a file. In other words: if you’re not getting thumbnails for certain types of files made on upload, then using Derivative Images won’t change that.
If that’s the case, that you never get them, there’s probably two things happening:
- For PDFs, ImageMagick uses another program, Ghostscript, to process PDFs, so that has to be installed on your server. Also, there’s sometimes a policy set for ImageMagick that prevents it from loading PDFs. You’d have to look into changing that policy or asking your host to change it if that’s the case.
- For MP4 and other video, ImageMagick uses the program FFMPEG to process the video. Like the previous point, it needs to be installed on the server for videos to work with ImageMagick.
If you do make changes such that the thumbnails for new files start working, that’s when you’d use the Derivative Images plugin to re-run the process on any files you have already uploaded that didn’t get thumbnails the first time around.
I installed Ghostscript, but still no thumbnails. However, FFMPEG works well and the video thumbnail is created.
I would guess this is ImageMagick’s policy.xml blocking this, then. It’s located at /etc/ImageMagick/policy.xml or somewhere similar (you can run convert -list policy to see what policies are being applied and what file they’re coming from).