WAV and Extended WAVE Formats Question

[Jack O'Sullivan]

I have some WAVE files that are currently being identified as both fmt/2 Broadcast Wave, and fmt/142 WAVEFORMATEX.

From looking at the file, I can see that it does in fact match both signatures, and it seems to me this will be true of many files that match the fmt/142 signature, but also have a BEXT chunk.

Am I right in thinking that this means that there should be a priority relationship between the two? I'm assuming fmt/142 should have priority over fmt/2? As there are already a batch of relationships between various wave files, I would really appreciate if someone who knows a bit more about wave files could confirm my assumption, or if this relationship is deliberately missing, explain why that might be.

Thanks in advance,

Jack

[Bertram Lyons]

Hi Jack --

I'm not sure how the priority relationship would work here. As far as the format specification for WAV is concerned, fmt/142 and fmt/2 are mutually exclusive, i.e., you could have one, both, or none in a given WAV file. The WAVEFORMATEX (fmt/142) is a variety of the standard WAV spec that defines the technical parameters available in the fmt chunk within the WAV file. There are sibling options, e.g., WAVEFORMATEXTENSIBLE, PCMWAVEFORMAT. Additonally, the BEXT chunk (fmt/2) is an optional chunk (totally unrelated to the three aforementioned) that provides additional parameters that were specified by the European Broadcast Union a number of years ago. The existence of this chunk within a WAVE file is what technically constitutes a "Broadcast Wave File" or BWF. 

In short, I think you'd be fine to mark these as separate indicators of the overall composition of your files.

Best --

Bert

__________________________________________________________

Bertram Lyons   New York | Wisconsin | Florida | Wyoming | Chile   202-430-4457 www.weareavp.com

[Jack O'Sullivan]

Hi Bert,

Thanks for the explanation. Can I just double check that I'm interpreting correctly;  you are saying it is valid to say that a given file may be both a Broadcast Wave and a WAVEFORMATEX, and as such DROID is correct to assign both format identifications to it.

Regards,

Jack

[Bertram Lyons]

Hi Jack --

Yes. It is valid that a given file may be both a Broadcast Wave (i.e., it has a BEXT chunk present), and conforms to a WAVEFORMATEX parameter configuration within the fmt chunk.

For example, a given WAV file may have this structure:

RIFF 'fmt ' chunk (16 bytes of data):

  AudioFormat (SubDirectory) -->

  + [BinaryData directory, 16 bytes]

  | Encoding = 1

  | NumChannels = 1

  | SampleRate = 96000

  | AvgBytesPerSec = 288000

  | BitsPerSample = 24

RIFF 'LIST_INFO' chunk (396 bytes of data):

  Info (SubDirectory) -->

  + [Info directory, 396 bytes]

  | Title = Given title of the recording

  | Subject = Given subject of the recording

  | Engineer = Digitized by JKP

  | Copyright = Public Domain

  | Artist = Name of the Artist

  | Keywords = One, Or, More, Keywords

  | Software = WaveLab 6.10

  | DateCreated = 4/17/2008

  | SourceForm = 1/4 in. tape

RIFF 'bext' chunk (602 bytes of data):

  BroadcastExtension (SubDirectory) -->

  + [BinaryData directory, 602 bytes]

  | Description = Broadcast description

  | Originator = Broadcast originator

  | OriginatorReference = Broadcast reference identifier

  | DateTimeOriginal = 2008-04-17

  | TimeReference = 0 0

  | BWFVersion = 1

RIFF 'PAD ' chunk (11218 bytes of data):

  Unknown_PAD = 

RIFF 'data' chunk (266207226 bytes of data):

In this example above, the BEXT chunk is a separate part of the file. Its presence leads to fmt/2 being called out. Its presence is optional. The WAV file remains functional without it.

In this example above, the fmt chunk is a separate part fo the file. Its presence and particular configuration leads to fmt/142 being called out. Its presence is mandatory, but its configuration is one of at least three possible configurations. This specific configuration is fmt/142. Another configuration of it is fmt/143, for example.

This file is both fmt/2 and fmt/142.

- Bert

__________________________________________________________

Bertram Lyons   New York | Wisconsin | Florida | Wyoming | Chile   202-430-4457 www.weareavp.com