Not all video formats are compatible for all mobile devices and browsers. The video gallery allows to play video .MOV and .MP4 video files, as we explain here.
In this way, if a participant uploads a video with a different format, this video will be published in the video gallery, but it won't be playable. This video will appear in the gallery identified with an arrow, which means that it can be downloaded, so that users can play in in their computer.
The administrator can also download the video from the list of entries, so that he can convert the video to a playable format, as we explain you here.