How to (re-)import to iMovie from DVD created with iDVD

Hello, I try to reimport a movie that I once exported to iDVD to iMovie or to Photos due to an HDD crash since exporting. But when I try to reimport, iMovie tells me to select a file, but all files on the DVD are greyed out, so I can´t choose them in order to reimport them. The original project in iMovie was lost due to the HDD crash.

Any hints or ideas on how to do that ? Thanks in advance !

I use:

MBP with El Capitan 10.11.6

iMovie 10.1.2

Photos 1.5

I will have probably used the iDVD version to create the DVD which was up to date in August 2014, don´t know which one this was.