What happens if you copy the “file” to your computer and play it locally, does it still crash?
In almost every instance where a media file (video) crashes during playback its because the file itself is corrupted and has nothing to do with the My Cloud. hat same file will crash if played locally on the computer. Many times if I reencode the video file (I use Handbrake) it solves the problem.
Also note that if using El Capitan OS on the Mac that others are reporting a variety of problems with El Capitan and the My Cloud.
