i use airAv too, perfect to stream and store file on the ipad for travel.
it read all the format, but he have problem with HD movies in Mkv (720p ...)
i have jailbreak it to allow me to install "XBMC Media Center".
Apple limit the acces to the hardware, so if you want an HD video without jailbreak it you need to convert it.
Or you can jailbreak it and install XBMC, it's perfect for streaming HD movie (1024p movie apparently are too 'big' for the wifi, but not sure)