E-mail from author follows:

I am the author of a video program for Windows called VirtualDub. Recently
a user reported a compatibility issue with AVI files written by ioquake3, a
Quake III Arena derivative for which you are listed as a contact on the web
page at http://icculus.org/quake3/.

I took a look at two of the AVIs produced by ioquake3, and both of them had
significant errors in RIFF structure -- specifically, the lengths of
several LIST chunks in the header were incorrect. This prevents both
VirtualDub's AVI parser and the Microsoft DirectShow AVI Splitter from
reading the files. I suspect that the problem is the following code in
ioquake3's cl_avi.c:

static ID_INLINE void END_CHUNK( void )
{
  int endIndex = bufIndex;

  if( afd.chunkStackTop <= 0 )
  {
    Com_Error( ERR_DROP, "ERROR: Bottom of chunkstack breached\n" );
  }

  afd.chunkStackTop--;
  bufIndex = afd.chunkStack[ afd.chunkStackTop ];
  bufIndex += 4;
  WRITE_4BYTES( endIndex - bufIndex - 1 );
  bufIndex = endIndex;
  bufIndex = PAD( bufIndex, 2 );
}


The length field for a LIST chunk should be set to the size of all
enclosing chunks plus the list type field, but not the LIST FOURCC itself
or the length field. Since the START_CHUNK() function pushes the location
of the chunk FOURCC onto the stack, I think the code should be this:

static ID_INLINE void END_CHUNK( void )
{
  int endIndex = bufIndex;

  if( afd.chunkStackTop <= 0 )
  {
    Com_Error( ERR_DROP, "ERROR: Bottom of chunkstack breached\n" );
  }

  afd.chunkStackTop--;
  bufIndex = afd.chunkStack[ afd.chunkStackTop ];
  WRITE_4BYTES( endIndex - bufIndex - 8 );
  bufIndex = endIndex;
  bufIndex = PAD( bufIndex, 2 );
}

This should improve the compatibility of AVI files produced by ioquake3
without side effects.