black screen with MP4

On a previous post it was written that problems with MP4s are due to “video decoding problem” but there were no details as to what types of codecs are required to work with this plugin.

Are there any explanations as to what kind of “decoding” is necessary? My Mp4 works in all other players but not in JW.

http://ww.wp.xz.cn/extend/plugins/cool-video-gallery/