Opening/converting DV movie files

I have some old DV Movie files that I'm trying to open, but QuickTime Player (10.5), iMovie (10.1.14), and Final Cut Pro (10.4.8) are all unable to open them. In April of last year I was able to convert one of the files (with QT Player if I remember right), but intervening updates seem to have removed that capability. How can I open them now?