Why mkvmerge (mkvtoolnix) shortens files when muxing ?

[Marus Nebunu]

I have a DVD with some video clips and I want to convert it (remux only, no recompression) in mkv files. I demuxed the DVD in separate audio and video streams with PgcDemux then I muxed back with mkvmerge in mkv container. The problem is that the mkv file is shorter than the DVD file (although the quality seems to be the same). For example, a 370MB DVD file is remuxed in 250MB mkv file. Why is that difference ? Because I do only remuxing not recompression. The file size should remain approximately the same.

[El Heggunte]

The container used in DVD-Video is the MPEG Program Stream, whose *overhead* is greater than the overhead of MP4 or Matroska.
The overhead of the transport streams (used in broadcasting and Blu-Ray discs) is even bigger than the overhead of MPG/VOB files.

[Marus Nebunu]

So this is normal and I don't need to worry about video quality being altered ?

[El Heggunte]

Yep.