Try downloading the video using an add-on called Flash Video Downloader. I use it in Firefox. There are videos like at Amazon and at Youtube that stream. You get dozens or hundreds of small video files. You can combine them all easily with Movavi Video Suite 18 then export as say a mp4.
Use VLC to play and capture. https://www.videolan.org/vlc/index.html Right click on toolbar and click on Advanced controls. You have a button there for screen capture. Go to Tools> Preferences> Video to change where to save.
I came across this issue with blu ray movies using the player I think was called WinDVD. The answer was to strip the encryption then convert to another type if you want like mp4 or use another player that allowed you to make captures.
For videos you have on a disc try the Leawo Blu-ray Player
https://www.leawo.org/tutorial/how-to-take-a-screenshot-on-windows-1373.html
Tools to use:
Best video converter out there. Quick and you can easily edit the video. Big TIP. Install the trial version then go to uninstall. They will popup a big 40% discount offer. Buy it.
Movavi Video Suite 18
https://www.movavi.com/suite/?asrc=main_menu
DVDFab
https://www.dvdfab.cn
Flash Video Downloader
https://addons.mozilla.org/en-US/firefox/addon/flash-video-downloader/