.WAV

Waveform Audio File Format

Introduction

WAV is the standard audio file of Windows, defined by Microsoft and IBM in 1991 as part of the Resource Interchange File Format (RIFF). Most WAV files hold uncompressed PCM audio: a plain list of sample values, the same data a sound card plays. That makes WAV large but simple and exact, and it is the usual format for recording, editing and exchanging audio between programs.

A WAV file can also hold compressed audio, such as ADPCM or µ-law, named by a format code in its header. Sizes in a WAV file are 32-bit, which limits a file to 4 GB. The Broadcast Wave Format adds a bext chunk with production details, and RF64 lifts the size limit. Files use the extension .wav, and sometimes .wave.

Software

Structure

A WAV file is one RIFF chunk with the form type WAVE. Inside it sit further chunks, each a four-character ID, a 32-bit little-endian size and the data, padded to an even length. See RIFF chunks.

Two chunks are required. The format chunk fmt says how the audio is encoded: the format code, channel count, sample rate and bits per sample. The data chunk data holds the samples, laid out as the format chunk describes. See Sample data. Other chunks are optional and carry metadata: a sample count, text tags, cue points, loop points and broadcast details. Files over 4 GB use RF64.

  1. 0RIFF chunk ID, file size minus 8, form type WAVE12 bytes
    1. 12fmt format code, channels, sample rate, byte rate, block align, bits per sample24 bytes
    2. 36data chunk header, then the samples8 bytes + samples
    3. …LIST, cue , smpl, bext … optional chunksvaries
The usual layout of a PCM WAV file, with its 44-byte header.

The format chunk decides how everything after it is read. This table shows how the common choices change the file.

AudioFormat codefmt sizeBlock alignSample values
8-bit mono PCM1161unsigned, 128 is silence
16-bit stereo PCM1164signed little-endian, left then right
24-bit stereo PCM1 or 0xFFFE16 or 406signed, 3 bytes each
32-bit float stereo316 or 188IEEE float, −1.0 to 1.0
5.1 surround, 24-bit0xFFFE4018six channels in channel-mask order
IMA ADPCM0x1120block size4-bit codes in blocks, with a fact chunk