401Dune

VOC File Format

By Ben Owen, 22/08/2009
Revision 2, 24/08/2009
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The VOC format is a fairly straightforward method of storing sound data. It was originally specific to Creative Soundblaster sound cards, but can sometimes be found today when recording sounds using a cheap MP3 player.

A .VOC file consists of a header followed by at least two data blocks, of which the last one will always be an End of Data marker.

header {
   char[20] FileType;  /* Must be "Creative Voice File" followed by an EOF
                        * character (0x1A). */
   Int16  DataOffset;  // Start position of the data block.
   Int16  FileVersion; /* File version. First byte is Major, second is
                        * Minor version number. This document is valid for
                        * values 0x010A and 0x0114, and apparently 256..*/
   Int16  IDcode;      // ~FileVersion + 0x1234 :- helps verify VOC file.
}

The data blocks always start with the same 4 bytes (excluding End of Data marker):

datablock {
   byte    BlockType;   // Type of block that follows.
   byte[3] BlockLength; // A 3-byte (24-bit) integer, gives block length.
}

Where BlockType is one of the following:

enum VocBlockType : byte {
   EndOfData     = 0; // End of Data marker. No following length field.

   NewSampleData = 1; /* Followed by two bytes indicating Sample Rate
                       * and Compression Type. The sample rate of the
                       * sound can be calculated using:
                       * Sample Rate = (-1000000)/(SR-256), where SR is
                       * the value read from the file. The compression
                       * type values are as follows:
                       * 0 : 8 bits - ie. uncompressed samples
                       * 1 : 4 bits packed
                       * 2 : 2.6 bits packed
                       * 3 : 2 bits packed
                       * These two bytes are then followed by
                       * (BlockLength - 2) bytes of sample data.
                       */

   SampleData     = 2; /* Sample data, use same properties as the
                        * preceeding block in the file.
                        */

   Silence        = 3; /* Followed by 3 bytes. First two indicate duration
                        * in terms of bytes. Third gives sample rate in
                        * the same manner as in NewSampleData.
                        */

   Marker         = 4; // Not covered.
   ASCIIText      = 5; // Not covered.
   RepeatStart    = 6; // Not covered.
   RepeatEnd      = 7; // Not covered.
   AdditionalInfo = 8; // Not covered.
   NewBlockType   = 9; // May be covered in a future revision.
}