I see the OP is using a Mac, not Windows, but the problem is almost certainly due to power management settings. When I started using MC for movies, they would always stop after 20 minutes. I knew the cause - the external USB drive would sleep after a period of inactivity, and MC couldn't wake it up fast enough to continue playback. It didn't happen with music because I didn't ever try to play a track long enough to let the HD sleep. I adjusted Windows power settings, to no avail, and I couldn't find a utility that would let me alter the drive's behaviour. Finally, in a last-ditch attempt I updated the OS from Windows 7 to Windows 10, and that gave me the control I needed to keep the USB port awake.
My advice to the OP is to experiment with the Mac. If you can't find an obvious power management setting, try something simple like using the Mac 10 minutes into the movie (open some files stored where the movie is stored, access the network).