MeGUI doesn't create the content by itself, it only lets the required encoder (xvid_encraw) run.
There are two different FourCCs: a) which encoder created the video stream {xvid}, b) which decoder should be used to decode it {DX50|XVID|...}. VfW based editors and analysis tools usually refer to the first one, while DirectShow based PC software players and also consumer players should refer to the second.
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