[MPlayer-users] REQ: Vdub compatibility for mencoder

[Timothy B. Terriberry]

When appending two AVI files, Virtual Dub requires a fairly strict match 
between the two stream headers. Currently, even with -oac copy -ovc 
copy, mencoder produces headers completely incompatible with the 
original file. This is unfortunate, as the error concealment features of 
libavcodec are very useful for splicing out corrupt segments of a file, 
re-encoding them with mencoder, and splicing them back in.

The first part of the problem (and the cause of -ova copy -ovc copy 
failure), is that mencoder does not correctly copy the frame rate 
parameters. Because of its internal use of floats, the frame rate in the 
final AVI is _always_ different from the input, often by a significant 
amount.

A second part of the problem is case sensitivity in the FOURCC codes. 
For example vcodec=msmpeg4 produces a stream with FOURCC "div3" instead 
of "DIV3". Vdub is not smart enough to match the two.

These are not the only problems, however. Even forcing the frame rates 
to be the same by manually fixing up the header afterwards and forcing 
the correct FOURCC with -ffourcc does not resolve the difference in 
stream headers between what is produced by any of the standard Windows 
codecs (DivX 3.11alpha, XviD, DivX 4/5), and the headers produced by 
mencoder with libavcodec. I've had success in the past just copying over 
random hex values from one header to the other, but do not remember 
specific values/offsets from the last time I got this to work (months ago).