MKVToolNix appyling compression?

I was told that files would not be compressed, however the first time I ran a file though, after being split, there was a different of 13,407KB, after changing the default value to not apply the lossless compression, I am still seeing a difference of 1000KB, is this normal? Is it being compressed at all? I also ran a file through without splitting it, and the output was still about 1000KB difference, so what did it do when I didn’t change any settings?


The only type of compression that MKVToolNix can apply is lossless compression for subtitles. This means there’s no loss of quality whatsoever with audio, video or subtitles.

That the file sizes differ is normal. Media containers such as Matroska are flexible (some more, some less); therefore the amount of container-related data differs.