Per microsoft AVI RIFF File Reference documentation: For chunk data blocks: The data is always padded to nearest WORD boundary. ckSize gives the size of the valid data in the chunk; it does not include the padding, the size of ckID, or the size of ckSize.
WORD data size 2 is bytes. gwavi.c Line 241 using a 4 byte pad. It should be 2. Also, the size of the pad is being added into the size of the chunk and it should not be.