matroska

Taken from the comments section of http://www.nyaa.se/?page=view&tid=480519

>Why not MKV?
It is a common misconception that mkv is at all better than mp4; They both offer the same potential of quality. While it is true that mp4 files tend not to be as good, it's not because they are mp4. It's just a correlation.
mka is seen as the "better" file extension only because it's less used and not as widely supported. Refusing to download something that isn't mkv is very elitist.
mp4 files also tend to be smaller, and with the same quality. This is because, as stated earlier, mp4 files are more widely supported. It is easier for a computer to store an mp4 file while using less space, just as it's easier for a computer to store a rar file in comparison to the files inside a rar file. It's because of compression.
The sound is also based on an mp3 format, which is much more compatible with mp4 since they both have mp in them. An mp3 sound file will not as well be compatible with an mkv because they only share one letter. It may seem like a weird reason but I assure you that each letter of an extension is like an RNA: A, U, C, and G. m fits to m, and so on like that.
My friend is a computer major and he told me this.