VOC Format

The Creative Voice File (.VOC) consists of a main header, followed by one or more data blocks. The file is in little Endian format.

Contents 1 Main header 2 Data blocks 2.1 0: Terminator 2.2 1: Sound data 2.3 2: Sound data (2) 2.4 3: Silence 2.5 4: Marker 2.6 5: Text 2.7 6: Repeat start 2.8 7: Repeat end 2.9 8: Extra information 2.10 9: Sound data (New format) 3 Source

Main header

Bytes	Value
0-18	"Creative Voice File"
19	0x1A
20-21	Size of the main header. Usually 0x1A 0x00
22-23	Version number. Usually 0x0A 0x01 (Old format) or 0x14 0x01 (New format)
24-25	"Checksum". This should equal version + 0x1234

Data blocks

All data blocks have a common header:

Bytes	Value
0	Block type
1-3	Block size, excluding the header

There are 10 different block types:

0: Terminator

This special block does not contain a size in the header. It is used to indicate the end of the file, though the file can end without it.

1: Sound data

Bytes	Value
0	Frequency divisor
1	Codec #, see below
2-n	Audio data

The sample rate of the file can be determined by:

Sample rate = 1000000/(256 - frequency divisor)

The codec can be one of the following:

Codec #	Name
8 bits unsigned PCM
0x01	4 bits to 8 bits Creative ADPCM
0x02	3 bits to 8 bits Creative ADPCM (AKA 2.6 bits)
0x03	2 bits to 8 bits Creative ADPCM
0x04	16 bits signed PCM
0x06	alaw
0x07	ulaw
0x0200	4 bits to 16 bits Creative ADPCM. Only valid in block type 9

2: Sound data (2)

Bytes	Value
2-n	Audio data

This block uses the same codec as block type 1.

3: Silence

Bytes	Value
0-1	Length of silence - 1
2-n	Frequency divisor (see block type 1)

4: Marker

Bytes	Value
0-1	Mark value

Apparently, this can be used to synchronize the sound file with an external animation.

5: Text

Bytes	Value
0-n	Text string, zero terminated

6: Repeat start

7: Repeat end

8: Extra information

9: Sound data (New format)

Source

This page was adapted from MultimediaWiki