This is a known issue with dvdplayer in Kodi - I get the exact same thing on some video files on my Mac Mini, so it’s not OSMC specific.
However there are some settings you could try changing that may help - one is to re-enable omxplayer, which has been off by default in the last few versions of OSMC on the Pi 2. This is in settings->Videos->Acceleration, make sure omxplayer is enabled. (omxplayer does not suffer from this wow and flutter issue)
Other options you could try are in Settings->Videos->Playback, try changing sync playback to display to off, or try changing A/V sync method to Adjust PLL. (You might need to try these options in conjunction with omxplayer)
Let us know if any of those help.