You should set a minimum length requirement for videos.
There are so many videos that are under 30 seconds that just take up space. It is conceivable that such a short video could contain something worth posting. But, establish should criteria for the very short videos or have a reviewer or something. I am not referencing the 15 second previews. I am talking about he really short videos that do not show much of anything.
Thanks for your suggestion, we are always keen to listen to our customers and to receive their feedback. Unfortunately we have no explanation to why the system sometimes accepts videos that are less than 60 seconds. We advise our users to upload videos 60 seconds or more so that their video does not fail during conversion.