why is video unplayable? [mencoder vs virtual dub]

This is good question

meizu converver and anything other based on mencodr produce unplayable file from some video

virutaldub not

So i take virutaldub with direct stream copy for audio and video, then i splitted file to short chunks (~1000 frames each) and noticed that only first one was unplayable and others was ok (maybe virtualdub don't need to generate some part of header for first fie and don't do so), but what part?

examples:

http://rori.parba.cz/not_working.avi
http://rori.parba.cz/working.avi

is there some better/more detailed analyzer for avi header then gspot and mplayer -v?

This is believed to be caused by corrupt data chunks at the start of the movie. Though it is not fully answered in detail, the BatMan Converter can solve it with its "repair" function.