Media Players couldn't play a .MKV file

a cooperator

Aug 7, 2012
Hi Everyone!
I have downloaded a .MKV file from internet, and it has file size of 35.7 MB. When I had tried opening it with some of Media Players, such as

Movie and TV, this error "Cannot play because the items's file format isn't supported" was shown.
Windows Media Player, this error "Windows Media Player encountered a problem while playing the file."
QQ player, the QQ player was automatically closed whenever I opened the file with it.
JetAudio, there is no response.
Media Player Classic, this error was shown.

However, when I converted the MKV file to MP4 file using Any Video Converter program, then the output .MP4 file was played well with either of the above Media players. However, the output .MP4 file became having a file size of 185 MB although the original input .MKV file was having a file size of 35.7 MB.

As a result, I am stumped by why all those Media Players couldn't play the .MKV file. If it was corrupted, defective, then the output .MP4 file would have been produced corruptly.