Sustainability of Digital Formats: Planning for Library of Congress Collections

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Broadcast WAVE Audio File Format, Version 2

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name EBU Broadcast Wave Format, Version 2

File format intended for the exchange of audio material between different broadcast environments and equipment based on different computer platforms. Based on the Microsoft WAVE audio file format, Broadcast Wave adds a required "Broadcast Audio Extension" (bext) chunk to hold the minimum information considered necessary for broadcast applications. Additional metadata chunks have also been developed; see Notes. More information is provided in the format description for WAVE_BWF_1 (version 1).

The most significant new element in version 2 is the inclusion of metadata pertaining to the measurement of loudness in the file. Additional information about this, and links to related standards and other informative documents, will be found on page 12 of Embedding Metadata in Digital Audio Files: Introductory Discussion for the Federal Agencies Guideline.

Production phase Used for content in initial, middle, and final states.
Relationship to other formats
    Modification of WAVE, WAVE Audio File Format
    May contain LPCM, Linear Pulse Code Modulated Audio (LPCM)
    May contain MPEG-1 and MPEG-2 Layer I Audio Encoding, not described at this Web site
    May contain MPEG_layer_2_audio, MPEG-1 and MPEG-2 Layer II Audio Encoding
    Has subtype WAVE_BWF_LPCM_2, Broadcast WAVE File Format, Version 2, with LPCM Audio
    Has earlier version EBU Broadcast Wave File Format (1997, sometimes called "Version 0"), not described at this Web site.
    Has earlier version WAVE_BWF_1, Broadcast WAVE Audio File Format, Version 1
    Has extension MBWF / RF64: An extended File Format for Audio, not described at this Web site at this time.
    Used by MXF_RDD48, MXF Archive and Preservation Format Registered Disclosure Document (SMPTE RDD 48)

Local use Explanation of format description terms

LC experience or existing holdings When reformatting analog sound recordings, the Broadcast WAVE format (either version), wrapping LPCM, is used as the archival master format for mono and stereo audio at the Packard Campus for Audio-Visual Conservation and by the American Folklife Center.
LC preference

The Broadcast WAVE format (either version), wrapping LPCM, is preferred as the archival master format for mono and stereo audio when reformatting analog sound recordings. The Library is a participant in the Federal Agencies Audio-Visual Working Group that published a recommended specification for BWF bext metadata conforming to version 1 in 2009, with an update conforming to version 2 in 2012.

The Library of Congress Recommended Formats Statement (RFS) includes WAVE file with embedded metadata (Broadcast WAVE) as a preferred format for media-independent audio works in digital form. The RFS does not specify versions of BWF.

Sustainability factors Explanation of format description terms

Disclosure Open standard developed as a refinement of the WAVE format by the European Broadcast Union (EBU), a standards developing organization.
    Documentation EBU Tech 3285 - Specification of the Broadcast Wave Format (BWF) - Version 2 - (2011). Other related EBU standards are listed in the format description for version 1.

Widely recommended, including as the preferred format for the delivery of music recordings to record companies in the Draft Recommendation for Delivery of Recorded Music Projects developed by the Delivery Specifications Committee of the Producer's and Engineer's Wing of the Recording Academy (National Academy of the Recording Arts and Sciences). Audio format specified in AES31-3, the Audio Engineering Society's specification for session project interchange, where LPCM encoding is implied but not specified.

Adoption of Broadcast wav files is strongly supported by the open source BWF MetaEdit tool which supports the FADGI Broadcast WAVE Metadata Embedding Guidelines. BWF MetaEdit was initially funded by the Library of Congress and FADGI (Federal Agencies Digital Guidelines Initiative); designed and led by AVPreserve; developed by MediaArea.

    Licensing and patents None.
Transparency The file format is transparent. For information on the transparency of the included audio encodings, see LPCM and MPEG_layer_II_audio. BWF metadata is human-readable.
Self-documentation The Broadcast Audio Extension (bext chunk) holds metadata identifying the originator and the date and time of creation, and technical-administrative metadata, e.g., about loudness.   Additional options for embedding metadata are outlined in the format description for version 1.

Accessibility Features

WAVE files have good support for accessibility features. Closed captions and transcriptions can be embedded within the Labeled Text chunk (ltxt) and identified as such with the 'Purpose' label. The specification includes the suggested Purpose value of 'capt' for closed-caption text and FADGI defines, in Guidelines for Embedding Metadata in Broadcast WAVE Files, the Purpose value of 'tran' for transcription. Overall, the optional Associated Data Chunk fields allows a mechanism to provide context for the audio data along the timeline which is helpful but it is not expressly designed for accessibility impacts.

In common practice, typically WAVE and other audio file content is supported by external caption and subtitle formats such as WebVTT. See W3C's Making Audio and Video Media Accessible for more general information about accessible sound and moving image media.

External dependencies None
Technical protection considerations None

Quality and functionality factors Explanation of format description terms

Normal rendering Supported
Fidelity (high audio resolution) Depends upon encoding; see WAVE_LPCM or MPEG_layer_II_audio.
Multiple channels May depend upon encoding; see WAVE_LPCM or MPEG_layer_II_audio. Note that multichannel audio is supported in the MBWF ("RF64 with a bext chunk") specification, EBU-TECH 3306, MBWF / RF64: An extended File Format for Audio (2009). Link available via Internet Archive.
Support for user-defined sounds, samples, and patches Not supported
Functionality beyond normal rendering Files greater than 4 GB in size may be produced using the MBWF ("RF64 with a bext chunk") specification, EBU-TECH 3306, MBWF / RF64: An extended File Format for Audio (2009), available via Internet Archive. See Notes.

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension wav
Internet Media Type See related format. 


Magic numbers Hex: 52 49 46 46 xx xx xx xx 57 41 56 45 xx 62 65 78 74 xx 02 00
ASCII: RIFF....WAVEfmt .. bext .. 2 (version)
Other NF00540
See NARA File Format Preservation Plan ID
Pronom PUID fmt/527
Wikidata Title ID Q27526504

Notes Explanation of format description terms


Four metadata chunks beyond bext have been established for Broadcast WAVE files. First is AES46 (initially standardized in 2002 and revised in 2007): AES standard for network and file transfer of audio Audio-file transfer and exchange Radio traffic audio delivery extension to the broadcast-WAVE-file format. Its purpose is stated as "an interchange medium by audio production and on-air delivery systems to exchange audio data . . . along with basic scheduling, traffic or continuity information." Second is axml, developed by the EBU in 2003, with a corollary schema called aXML. This is potentially useful but seems not to have been widely adopted. See Specification of the Broadcast Wave Format; A Format for Audio Data Files in Broadcasting; Supplement 5: <axml> Chunk, accessed April 26, 2022. Third is iXML, developed by a British trade group, the Institute of Broadcast Sound (IBS), a group of audio hardware and software manufacturers who sought to facilitate transfer of production metadata across systems and now maintained by Gallery UK. The current version of the iXML Specification Revision 3.01 is dated 28th October 2021; earlier versions of the specification can be found in the Internet Archive Wayback machine. iXML was being developed as a standard by the Audio Engineering Society (AES) working group SC-03-06 as AES-X155: Production recording metadata set (iXML) but this does not seem to have been finalized. Comments welcome. Fourth is an implementation of Adobe's XMP Specification. This structure can exist as a "sidecar" file or be embedded in a variety of content-essence files, including WAVE (need not be Broadcast WAVE). XMP has been widely adopted by professional photographers because it is well supported in the ubiquitous family of Adobe imaging software, where it generally takes the form of the news-oriented metadata standard from International Press and Telecommunications Council (IPTC). Adobe and the IPTC are actively exploring ways to expand the use of XMP among audio and video producers, especially in the field of journalism.

From the Wikipedia article RF64 (consulted October 26, 2012): "RF64 is a BWF-compatible multichannel file format enabling file sizes to exceed 4 GB. It has been specified by the European Broadcasting Union. The file format is designed to meet the requirements for multichannel sound in broadcasting and audio archiving. It is based on the Microsoft RIFF/WAVE format and Wave Format Extensible for multichannel parameters. Additions are made to the basic specification to allow for more than 4 GB file sizes when needed (the new maximum filesize is now approximately 16 exabytes). . . . In its basic form, the 32-bit chunk size field at offset 4 in the file is set to -1 (0xFFFFFFFF), and immediately following that a new 'DS64' chunk is inserted (before the FMT chunk). This new DS64 chunk will contain the 64-bit sizes of the DATA chunk(s), using a simple sequential table mechanism to point to additional DATA chunks. The first 4 bytes of the file are then changed from 'RIFF' to 'RF64'. . . . An RF64 file with a bext chunk becomes an MBWF-file. The terms ‘RF64’ and ‘MBWF’ can then be considered synonymous.


There have been three iterations of the BWF format under the general specification number EBU Tech 3285. Version 0 (as it came to be called) was published in 1997. Version 1, which differs from Version 0 in the use of 64 of the 254 reserved bytes to contain a SMPTE UMID identifier, was published July 2001. Version 1 was followed by six supplements with additional information. Version 2 references these supplements and adds elements that pertain to loudness metadata.

How can you identify the version? One method is to take advantage of the facts that (a) the bext chunks in Version 0 files do not have a space reserved for the UMID and (b) the bext chunks for neither Version 0 or Version 1 files have spaces for loudness metadata. Thus, if a file has BEXT data but no UMID or loudness values, it is Version 0. (The version 0 value for the BEXT Version element is not specified in EBU Tech 3285; the Broadcast WAVE guideline from the Federal Agencies Digital Guideline Initiative (FADGI) recommends using the value 0000h.) If a file has BEXT data and a UMID value but no loudness values, it is Version 1. (EBU specifies 0001h as the value for the Version element.) If a file has BEXT data and loudness values, it is Version 2. (EBU specifies 0002h as the value for the Version element.)

Format specifications Explanation of format description terms

Useful references


Last Updated: 06/10/2024