BLDD spec, version 2.

A .BLDD file consists of a header followed by a block stream.

Header:
type             length(bytes)         usual value                 Purpose
char[16]         16                    "VDDCompactedFile"    Magic string to
identify the file type.
unsigned char    1                     0                     Minimum version
needed to decode. 
unsigned int     4                     >=4                   Length (bytes) of the optional header extension immediatly following this field.
                                                             Minimum of 4, as the first four bytes of a header extension identify their function.
                                                             A value of 0 indicates that there are no further extensions, and the blockstream follows immediatly.
                                                             If non-zero, skip the appropriate number of bytes and repeat until zero encountered.

So far, only one header extension is defined:
Block size header (Requires minimum decode version byte >=1)
char[4]		4			"BKSZ"			Identifies header type.
unsigned int	4			Usually a power of 2.	Block size. In the absence of this header, default to 512.


Blockstream:
  Each block is 512 bytes long and numbered starting at zero. If the block starts with any value other than a 0xE7 byte, then it is an unprocessed block which could not be deduplicated and should be simply output as-is. If the first byte is 0xE7, then the following byte specifies a command for the correct handling of this block.

Value   Following payload length           meaning
0xE7	blocksize                           This block really does start with 0xE7. It was just nessicary to escape it.
0x01    4                                  This block is a duplicate of the block identified in the following unsigned 32-bit integer
0x02    8                                  As with 0x01, except with a 64-bit integer. This should only ever be encountered for files of length >2TB.
0x03	0                                  This block is null. Output 512 nulls.
0x04    4+(n*blocksize)                    Unescaped data follows. 32-bit int specifies number of blocks. This is not supported by the reference encoder.
0x05	0                                  This block is a duplicate sourced from the block immediatly following the last block used as a reference.
                                           In an encoded file, this does mean potentially very long strings of paired 0xE705 characters - conventional compression will reduce them.
0x06	4                                  End of file marker. Followed by at least four bytes, usually zero, for future use in adding 'tail' fields. Optional.