Originally Posted by wierdo124
I do'nt know everything about formats but I'm fairly knowledgeable
I'm sure plenty of people on OCN know far more than that.
H264 (AKA X264)(mkvs, mp4s etc) videos have more compression though and almost always require more processing power to play than an Xvid video (avi). Heck, N7 could probably play an avi while sipping power on its companion core.
Technically, you can have MPEG-4 Part 2 (SP/ASP) such as DivX and Xvid in MKV and MP4 containers. Indeed, early iPod MP4 videos just used MPEG-4 SP. AVI is also just a container and can hold MPEG-4 Part 10 (AVC/H.264) although variable framerate support can make things tricky. H.264 uses more efficient compression compared to DivX/Xvid so at a given bitrate/file size, the H.264 video will look better compared to DivX/Xvid.
Of course there are various encoding profiles and options for H.264 and most devices have dedicated hardware video decode processors because the wimpy ARM CPU on these things wouldn't be able to handle H.264 playback otherwise. That's also part of the reason why tablets can't play everything a PC using a software decoder is able to. If the hardware decoder can't support a particular profile/option (e.g. Hi10p), that's usually it. You're unlikely to be able to fall back to software decoding as there's just not enough processing power.
MKV and FLAC aren't really equivalent. FLAC = Free Lossless Audio Codec. It's actually both container and codec. MKV is just a container and can have multiple streams stored in it including H.264, Xvid, FLAC, DTS, AC3, subtitles, fonts, etc.