Most are SRT. Which if i remember well vlc for ipad was not handling.
They're automatically loaded by AVPlayerHD, assuming their filename is the same as the main video file.
If you have more than one sub file for a video (in different langs) and want to switch between them, you'll either need to rename them right on your iPad before starting playback or switch to another player with manual SRT association capabilities (e.g., yaPlayer).
----------
This is why I in no way recommend any "reviews" published in AppStore. They're almost all garbage and in no way should be trusted.
BTW, I've quickly looked up the ratings of current versions of the top three generic players, AVPlayerHD, GoodPlayer, It's Playing.
GoodPlayer: 1.5 stars - while it doesn't support AC3 and has a lower-efficiency H.264 decoder, it's still one of the best, most standards-compliant player, partcularly excellent (in most cases, best in all AppStore apps) at streaming. Deserves a much-much better rating.
AVPlayerHD: 3.5 stars - another non-deserved (bad) rating. AVPlayerHD deserves at least 4.5 stars when it comes to decoder quality / speed, standards compliance etc. Of course it has a lot of missing functionality (lack of e.g. streaming support) but what it does it does excellently and, in many cases, by far the best in all AppStore apps (e.g., MKV playback). And it's the only choice for AC3 people (CineXPlayer, the other AC3-capable player, is significantly inferior).
It's Playing: 2 stars: another top player with absolutely excellent and unique DSP support and significantly better streaming support than that of AVPLayerHD. Deserves a much better rating.
----------
All right, well said. So you're saying that if we use the settings you recommended in your review, playback will essentially be as flawless as anything else? I've always converted my .mkv's to play on iPad and got so sick of it I just stopped doing it unless it was an "emergency" like a flight or something.
If I use this app, will it be as comfortable as, say, playing an .mkv on VLC on the mac mini? Or will there be a bit more lag but "hardly noticeable"?
For direct MKV playback (assuming their video track is H.264 and not something else - for example VC-1), AVPlayerHD is by far the best and most stuttering-free player, particularly now that BUZZ Player and HD Player Pro stopped supporting AC3 (and BUZZ have never stupported hardware-assisted MKV playback of videos with DTS audio).
There is only one case you should look somewhere else: when you
badly need runtime DSP's (brightness / audio boosting). Then, your only choice is It's Playing. Its DSP's are phenomenal but, generally, plays back MKV's a bit more stuttering.
Of course, if you can jailbreak (iPad 1 on anything or 2/3 on 5.1.1), you can also give a try to RushPlayer+ and XBMC, they're both great and free(!), unlike the above-mentioned AppStore players. (Well, RushPlayer+ isn't free but, unless you need e.g. filelist sortability, you can live without purchasing its unlock IAP. The free version has no playback-related restrictions, only those of menu-related features.)