Hi Mosu!
Not so long ago I discovered (official?)tool called
mkvalidator. Not sure why I need it but I tried it just out of curiosity and found that it displays a lot of warnings for files muxed with mkvmerge. like this: "WRN0C0: First Block for video track #1 in Cluster at 69826954 is not a keyframe" However there is also some errors sometimes.
So the question is, does this validator actually valid?