Which player are you using? What is the format of the video, ie is it avi mp4 or other format?
I play mostly mp4,s without any issue with the video player. I also have a lot of mkv's and then I have some with sub titles. For those I have been using oplayer hd or gplayer and so far I have had no problems. You could also try rebooting the iPad which will fix some of these little issues. Occasionally I have had the apps store stop functioning fully, can search but when it gives me the list I can't select anything and rebooting fixes it.