Unfortunately, more and more players (my last, three-day-old, related article reporting on no less than five(!) players' doing the same) end up dropping AC-3 (and related) audio support, meaning the inability to play back the audio in a lot of videos: all AVCHD ones (camera MTS files etc.), about half of MKV's (AC-3 is very popular with MKV's, the other popular audio format being DTS), all ATSC (U.S.) digital TV broadcast recordings, a lot of AVI's etc. - as is also mentioned by THIS, RushPlayer-AC-3-drop-related post.
The newest victims are:
- RushPlayer - a decent player (but not as good as the top-end ones)
- VM Player (HD) - an, in my opinion, pretty mediocre player.
HD Player Pro, which I, for hardware MKV playback, highly recommended in my recent, dedicated article, fortunately, "only" dropped the not-that-common Meridian Lossless Packing (MLP) and E-AC-3 support; that is, the new version does support AC-3.
An AppStore update list showing all this (except for the somewhat earlier RushPlayer dumbing-down):
Note that the "unleashed" and, because of not being restricted by Apple's overly restrictive (and, IMHO, in a lot of cases pretty unnecessary) AppStore rules, far superior Cydia version of RushPlayer, RushPlayer+ (review; note the + sign!) still does support AC3. If you absolutely want to stick with the RushPlayer interface, consider switching to that version - if your iDevice is jailbroken, that is. Note that the free version is preferctly usable for playback. Unfortunately, the developer of the app still uses its own, very restrictive and, in my opinion, unreliable in-app purchase method locking the player's license to one device only. I really hope he switches to the standard Cydia purchasing mechanism some time allowing to easily reinstall the app on another device; until then, I don't really recommend purchasing the app.
Also note that, should your iDevice not be jailbroken and/or you are ready to switch to another player, It's Playing, an absolutely stunning player (latest review), (still?) supports AC-3. You really should give it a try - not only because of AC-3.
Finally, as you can see by comparing the above update list and my previous HD Player Pro review, the only change in the just-released, new version (5.0.2) is the removal of the Dolby support (again, except for the "base" AC-3). That is, the traditional "back up and restore the old 5.0.1 IPA file" method of keeping the E-AC-3 / MLP support (by securing the old version) by sticking with version 5.0.1 will work just fine and you won't lose any new functionality / bugixes.