Broadcast Wave Format

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Broadcast Wave Format
Filename extension .wav
Developed by European Broadcast Union (EBU)
Initial release 1997 (1997)
Latest release Version 2  / May 2011; 3 years ago (2011-05)
Type of format audio file format, container format
Extended from WAV
Standard EBU - TECH 3285 Specification of the Broadcast Wave Format (BWF)
Website Broadcast Wave Format (BWF) user guide

Broadcast Wave Format (BWF) is an extension of the popular Microsoft WAVE audio format and is the recording format of most file-based non-linear digital recorders used for motion picture, radio and television production.

It was first specified by the European Broadcasting Union in 1997, and updated in 2001 and 2003.

The purpose of this file format is the addition of metadata to facilitate the seamless exchange of sound data between different computer platforms and applications. It specifies the format of metadata, allowing audio processing elements to identify themselves, document their activities, and permits synchronization with other recordings. This metadata is stored as extension chunks in a standard digital audio WAV file.

Files conforming to the Broadcast Wave specification have names ending with the extension .WAV.

In addition to the common WAVE chunks, the following extension chunks can appear in a Broadcast Wave file:

  • Original Bext chunk (Broadcast Extension - 'bext')
  • iXML chunk ('iXML')
  • Quality chunk ('qlty')
  • MPEG audio extension chunk ('mext')
  • Peak Envelope chunk ('levl')
  • link chunk ('link')
  • axml chunk ('axml')

For more information, see EBU BWF User Guide

WAV compatibility[edit]

Since the only difference between a BWF and a "normal" WAV is the extended information in the file header (Bext-Chunk, Coding-History, etc...), a BWF does not require a special player for playback.

Unfortunately, this compatibility also preserves the filesize limitation that WAV files have (4 GiB in theory, 2 GiB in practice because most implementations use signed integer). In order to be able to store audio which would exceed this limit, 2 different chunks exist allowing the audio material to be spread across several files: cont & link (see list above)

Since there is no official naming convention for these subsequent files, and it is still desirable to see at a glance which ones belong to a continuous piece of audio, a lot of programs apply a numbering scheme to the file suffix: .wav, .w01, .w02, ..., .wNN.

Each of those segments is a regular Wave/BWF file, but players that are aware of the continue/link chunk will treat all segments as one single, long piece of audio when opening the first segment ".wav".

As an extension, RF64 is a BWF-compatible multichannel file format enabling file sizes to exceed 4 GiB that has been specified in 2006.

The axml chunk allows users to incorporate data compliant with the XML format with the audio; the chunk may contain data fragments from one or more schema.

BWF is specified for use in MXF by SMPTE standard 382.

BWF is specified for use in AES31.

See also[edit]

External links[edit]