I'm using SS v. 2.3.4 and I have a problem to upload video. I create a gallery Page and I set video extension. When I try to upload video SS seems to upload and then I have blank page..why?? My video is 16MB. Id this the problem?
File size or your server not being able to encode the video (if you are trying to do so) seems the most likely problems.
Can you get any errors from PHP? You can check this article to get more error info: http://www.leftandmain.com/silverstripe-tips/2010/09/08/8-common-silverstripe-errors-explained-and-solved/