Wrong duration - play length MP4's

[lokii]

This is more of a how-does-this-work question. I am converting files so an old player can play them. MeGUI actually fails - but I really don't care. They work with VLC converting them. They do play, but the wrong duration/play time shows up. They will play - past this point, but it's annoying.

They play just fine in VLC on my computer. But I'm trying to watch them on my TV on an old player. I also have an older media player on my computer that shows the same problem - so it must have to do with older players and the way they process the files.

So - the question really is - how is the duration calculated? In this instance the time seems about half. Also - for short videos everything is fine - so something is happening only on longer ones. Know how this gets coded may help me fix it as I can edit the data in the file manually.

[lokii]

I found a solution, but did not really find out what the duration problem is... I went back to MeGUI, and ran the One-Click with my profile that works in most cases. It fails - just says with "1 error", no real info besides that. However the interim MKV file it makes is there. So I run the same profile with One-Click and it works. So the problem is with this file and the MKV file (or the dummy folder it is in) not being recognized in the process. Other files work just fine. This produces files that can be viewed perfectly in my outdated box attached to the TV.

[Zathor]

If you provide more details (logs, sample file) I may be able to fix it.