I found that ogg vorbis don't sync. with ogg theora
sample was uploaded before, that is [dmhy][onegai_twins][dvd_vol3_sp2].ogg
in this file, first 6 sec. is mute and ogg vorbis is 0kbps. in realplayer 10 it can sync. correctly but in vlc it jumps to 00:06 and playback the sound and then ogg theora still playbacking the video in the first 6 sec. and then the video jumps to 00:12 and sync. the sound again. that means 6 sec. of video is cutted out and the playback time is shortened.