Mencoder and VLC MJPG codec. Documentation?

[seabhcan]

Mencoder has a lovely option for converting a mjpeg file into an avi file with an 'MJPG' codec that plays in VLC.

The command line to do this is:

mencoder filename.mjpeg -oac copy -ovc copy -o outputfile.avi -speed 0.3

where 0.3 is the ratio of the desired play framerate to the default 25 fps. All this does is make a copy of the mjpeg file, put an avi header on top and at the end, what seems to be an index of the frame positions in the file.

I want to replicate this in my own code, but I can't find documentation anywhere. What is the exact format of the index section? The header has extra filler bytes in it for some reason - whats this about?

Anyone know where I can find documentation? Both mencoder and vlc seem to have this codec built in.

[hech54]

I just use VDub with MJPEG video.