Matroska

Matroska is usually found as .mkv files (matroska video).whenever you play a movie on your PC, without even noticing it, you are always playing at least one video stream and one audio stream at the same time. As it is not very practible to have to handle 2 different files for that, lets say an MP3 audio file and another file containing the video, you pack both into a single file by using a so-called container format file, comparable to a ZIP file. This container and the software coming with it take care of a lot of important functions, like the correct timing of the audio and video playback when the file is played ( opened ). ZIP or RAR could be a perfect container to pack one or more audio/video streams together into one single file for distribution, but WinZIP certainly wouldnt care about the correct timing of the these streams on playback ...
Known containers are the good old AVI ( most DivX movies you will get will have an .avi extension ), or the MPEG container ( .mpg , .mpeg ), Quicktime ( .mov ), Realmedia ( .rm ), MP4 ( .mp4 ), etc. .
The matroska project is a free, opensource alternative to all of them, and aiming to be able to offer a lot of features that others dont have have ( look at their homepage again ).

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