WAVE PCM soundfile format

The WAVE file format is a subset of Microsoft's RIFF specification for the storage of multimedia files. A RIFF file starts out with a file header followed by a sequence of data chunks. A WAVE file is often just a RIFF file with a single "WAVE" chunk which consists of two sub-chunks -- a "fmt " chunk specifying the data format and a "data" chunk containing the actual sample data. Call this form the "Canonical form". Who knows how it really all works.

I use the standard WAVE format as created by the sox program:

Offset  Size  Name             Description



The canonical WAVE format starts with the RIFF header:

0         4   ChunkID          Contains the letters "RIFF" in ASCII form

                               (0x52494646 big-endian form).

4         4   ChunkSize        36 + SubChunk2Size, or more precisely:

                               4 + (8 + SubChunk1Size) + (8 + SubChunk2Size)

                               This is the size of the rest of the chunk

                               following this number.  This is the size of the

                               entire file in bytes minus 8 bytes for the

                               two fields not included in this count:

                               ChunkID and ChunkSize.

8         4   Format           Contains the letters "WAVE"

                               (0x57415645 big-endian form).
The "WAVE" format consists of two subchunks: "fmt " and "data":

The "fmt " subchunk describes the sound data's format:
12        4   Subchunk1ID      Contains the letters "fmt "

                               (0x666d7420 big-endian form).

16        4   Subchunk1Size    16 for PCM.  This is the size of the

                               rest of the Subchunk which follows this number.

20        2   AudioFormat      PCM = 1 (i.e. Linear quantization)

                               Values other than 1 indicate some

                               form of compression.

22        2   NumChannels      Mono = 1, Stereo = 2, etc.

24        4   SampleRate       8000, 44100, etc.

28        4   ByteRate         == SampleRate * NumChannels * BitsPerSample/8

32        2   BlockAlign       == NumChannels * BitsPerSample/8

                               The number of bytes for one sample including

                               all channels. I wonder what happens when

                               this number isn't an integer?

34        2   BitsPerSample    8 bits = 8, 16 bits = 16, etc.

          2   ExtraParamSize   if PCM, then doesn't exist

          X   ExtraParams      space for extra parameters
The "data" subchunk contains the size of the data and the actual sound:
36        4   Subchunk2ID      Contains the letters "data"

                               (0x64617461 big-endian form).

40        4   Subchunk2Size    == NumSamples * NumChannels * BitsPerSample/8

                               This is the number of bytes in the data.

                               You can also think of this as the size

                               of the read of the subchunk following this

                               number.

44        *   Data             The actual sound data.

As an example, here are the opening 72 bytes of a WAVE file with bytes shown as hexadecimal numbers:

52 49 46 46 24 08 00 00 57 41 56 45 66 6d 74 20 10 00 00 00 01 00 02 00 

22 56 00 00 88 58 01 00 04 00 10 00 64 61 74 61 00 08 00 00 00 00 00 00 

24 17 1e f3 3c 13 3c 14 16 f9 18 f9 34 e7 23 a6 3c f2 24 f2 11 ce 1a 0d 

Here is the interpretation of these bytes as a WAVE soundfile: