.WV File Format – Sub-blocks

Sub-block header

The byte length is twice the word count, minus one with the odd flag. Data is padded to an even length, so the next sub-block starts on an even byte.

An unknown ID without the optional bit makes the reference library reject the block.

Worked example

Decorrelation terms with one term, 18, and a delta of 2. The term byte is (18 + 5) | (2 << 5), which is 0x57. It is one byte, so the odd flag is set and a padding byte follows:

42 01 57 00   id 0x02 | ID_ODD_SIZE, 1 word, term byte, padding

Sub-block IDs

Bit streams

The WV and WVC streams have a nonzero, even length, and hold nothing but the bit stream. The WVX stream is longer than 4 bytes and even: it starts with a 32-bit little-endian CRC, and the bit stream starts at offset 4.

The newer WVX form 0x2C reads two 5-bit fields from the start of the bit stream. For floating point these are the minimum shifted zeros and the maximum shifted ones; otherwise one field gives the largest integer width.

Channel information

The payload of ID_CHANNEL_INFO is 1 to 7 bytes. A length of 6 or more is the newer form.

The channel count cannot exceed twice the stream count, and the mask cannot have more bits than there are channels. There can be at most 4,096 streams.

ID_CHANNEL_IDENTITIES holds one byte for each channel. No byte may be 0; 0xFF means unknown.

Configuration

Other payloads

The block checksum

The payload is 2 or 4 bytes, never odd. It is calculated over the 16-bit little-endian words of the block, from its first byte up to, but not including, this sub-block’s own header:

csum = 0xFFFFFFFF
for each word w:  csum = csum × 3 + w
4-byte payload:   compare csum
2-byte payload:   csum ^= csum >> 16, then compare the low 16 bits