Thanks for your immediate answers. Not only a nice app, but fast support, too...
So, if it is MediaInfo, that is used to fetch the length of an AVI- or MKV-file (did I understand that right?), then MediaInfo gets the seconds, too. Perhaps it behaves different with different file types? Didn't try it with VOBs till now, cause I'm still quite new to PVD... Within PVD the duration must be stored to its full extend, cause it is displayed as 01:48:43, for example (in preferences "Use minutes for duration field" must be unchecked to see this, of course). Sometimes audio streams are longer than the video stream, and even that is recognised and the duration reported seems to always represent the duration of the longest stream. I love that!
And I'd love to be able to export it...