Could someone please tell me how to watch lets say a video before it has completely finished to make sure file is okay and that there is actually something there. Suppose you have about 50% or more how can you preview it so that if its corrupt or wrong file you can stop download.Appreciate any help you can offer, I am a newbee so hope I posted this ? in right spot. I catch on quick just need a few pointers.

Thank you so much
J