BWF metadata explained: bext, iXML and the data hiding in your WAV files

A WAV file straight out of a consumer app is basically raw samples with a header. A WAV file out of a field recorder is a Broadcast Wave Format file, and it carries a second life: who recorded it, when, at what timecode, on which scene and take, with which microphone on which track.

What Broadcast Wave Format actually is

BWF is not a different format. It is a standard WAV with extra chunks added, defined by the EBU. Any player that reads WAV reads a BWF file. Players that understand the extra chunks get the production data as a bonus.

The bext chunk

The broadcast extension chunk is the original BWF addition. It holds:

• Description, a free text field where recorders often write scene, take and notes.
• Originator and originator reference, identifying the device and the recording session.
• Origination date and time.
• Time reference, the sample count since midnight, which is how timecode is stored in a WAV.
• Coding history, a log of format changes applied to the file.

The time reference field is the important one. It is not a timecode string, it is a sample count. Divide it by the sample rate and you get seconds since midnight, which your NLE converts back into hours, minutes, seconds and frames using the project frame rate.

The iXML chunk

iXML is a small XML document embedded in the file. It is where modern recorders store structured production metadata, and it is far richer than bext.

• Project, scene, take, tape and circled take status.
• A full TRACK_LIST with a name for each channel, for example Boom, Lav Marie, Plant Kitchen, Mix L, Mix R.
• Frame rate, timecode flags and speed information.
• Notes from the sound mixer, which frequently explain why a take sounds the way it does.

Why the track list is the most useful field on set

The TRACK_LIST is what turns an anonymous 8 channel file into a readable session. When a splitter or a DAW reads it, channel 3 stops being channel 3 and becomes Lav Marie. Everything downstream, from filenames to timeline track labels, inherits that clarity.

Our audio inspector reads bext and iXML directly in the browser and shows you the scene, take, timecode, channel layout and per track names without opening a DAW. If a file arrives with no metadata at all, that itself is useful information: it usually means the file has been re-encoded somewhere and the production data was stripped.

How metadata gets lost

Exporting through a video editor, converting with a generic online tool, or bouncing to a new file will often discard bext and iXML. If you need the metadata preserved, work from the original masters and use tools that copy the chunks rather than rewrite the file from scratch.