[pawel]

VOB is a container for mpg format/file. It's rather hard to state if an mpg file was not twice re-encoded but of course if not done well it can be blurry, may have visible compression artefacts (low bitrate). Everything depends on the source material, what codec and in what setting is used to encode to mpg.

Edit: if the mpg file is smaller than VOBs (all VOBs containing the corresponding video and audio) it means that it is encoded in lower bitrate and/or screen size - it can be a VCD or SVCD for example.