apologies for the necro-post.
It's really the casino bums whom are responsible. the video is probably re-encoded from an already compressed source (meaning these bastards would just download it somewhere else) AND re-encoded USUALLY using a different framerate + audio codec + video compression rate. what these fucking useless bums don't get is that audio re-conversion and re-compression from within video would ALWAYS cause them to go out of sync, since the re-encoding is probably done on a canned program that has a generic setting for everything.
It's best to not download nor support them at all. besides, JAV really doesn't cost all that much than an audio CD, even online outlets like R18 and DMM stream digital copies at 3k to 6k compression rate - of which you can easily just do a video capture if you don't want the DRM hangup.
edit: their stuff are FAR from original rips, they downloaded all their stuff for free and slapped all that intrusive ugly ads and watermarks everywhere. which makes it even more unacceptable. these people are the reason why i refuse to put up torrents of my DVD rips anymore.