Broadcast Wave Format

Broadcast Wave Format (BWF) is an extension of the popular Microsoft WAV 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. It has been accepted as the ITU recommendation ITU-R BS.1352-3, Annex 1.

Broadcast Wave Format
Filename extension
  • .bwf
  • .wav
Internet media typeaudio/x-wav
Developed byEuropean Broadcast Union (EBU)
Initial release1997 (1997)
Latest release
Version 2
May 2011 (2011-05)
Type of formataudio file format, container format
Extended fromWAV
Extended toRF64
Standard
WebsiteBroadcast Wave Format (BWF) user guide

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 supports timecode to enable synchronization with other recordings. This metadata is stored as extension chunks in a standard digital audio WAV file.

BWF is the recommended format for digitizing sound files by the International Association of Sound and Audiovisual Archives.[1]

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

Details

In addition to the common WAVE chunks, the following extension chunks can appear in a Broadcast Wave file:[2]

  • 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')

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 GB of audio data per data chunk). 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 GB that has been specified in 2006.

The axml (additional XML) 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.

In August 2012, the European Broadcasting Union published a specification for embedding International Standard Recording Code (ISRC) in the axml chunk of the Broadcast Wave Format.

BWF is specified for use in MXF by SMPTE standard 382. BWF is specified for use in AES31.

See also

References
  1. IASA Technical Committee, Guidelines on the Production and Preservation of Digital Audio Objects (2009). Bradley, Kevin (ed.). Guidelines on the Production and Preservation of Digital Audio Objects (2nd ed.). Auckland Park, South Africa: International Association of Sound and Audio Visual Archives. ISBN 9789197619226.
  2. "EBU BWF User Guide" (PDF).
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