Video seen jumping
First, good morning to all.
I have a problem, my video saved to an external hardisk are seen in shots and jumping, whether they are downloaded from the iPhone or edited with iMovie, both in mp4 or mov. I do not know what to do to be able to see them, I have an iMac (27-inch, Mid 2010) OSX Yosemite 10.10.4 - Processor 3.2 GHz Intel Core i3 - Memory 12 GB 1333 MHz DDR3. I hope I have given you all the information you need and someone can tell me how to fix it. Waiting for an answer thank you in advance and regards
Piera
iMac, OS X Mountain Lion (10.8.4)