Dude just needed a piece of information. I always wanted to ask this question to somebody. Sometimes I find some movie files which say AC3 5.1 What exactly are these? They seem to be around 1.5 to 2.1 GB. I guess since the size is more, quality would also be better. Any inputs? And what about x264 which can be mkv or mp4. This always seems to be better in audio and video quality. Only down point being that it can't be played on a regular DVD player.
Sorry folks for off topic discussion!
AC3, in general, is another name for Dolby Digital. It's a audio compression technology. AC3 5.1 states that it retains the whole 5.1 channel effect ripped from a normal DVD. The higher quality rips, usually the ones with 2+ discs, may have AC 5.1 encoding on them. These are perfect to achieve a proper 5.1 channel surround sound. The increased size is also because of the audio bitrate. Pick any movie of 2CD version & you'll find that it usually has a very high audio bitrate compared to a 1CD version.
The .mkv & .mp4 are usually containers for storing video, audio & subtitles. They can't be played on normal DVD players with DivX/XviD support is merely because they aren't supported containers. They can only played by supported players like WD HD Media Player. It supports a wide array of formats including Matroska.