CODEWITHSUNDEEP
audio
PGupta
PGupta

Reputation: 215

Distinguish between PCM and BWF file format?

How can we distinguish between PCM and BWF format?

Is it necessary for BWF to have "bext" header?

I have some streams that don't have "bext" header but contains "JUNK" header... Are these files BWF files?

Thanks you.

Upvotes: 0

Views: 1664

Answers (3)

Herbie
Herbie

Reputation: 11

Yes. The 'bext' chunk is what distinguishes a BWF file from a wav file.
Some manufacturers actually use '.bwf' as a file extension but mostly the '.wav' extension will be used. It is only the presence of this chunk that makes the difference.

Other chunks can also be present and a well designed player will ignore chunks that it doesn't recognize.

Generally the 'data' chunk containing the audio data will be the last one in the file. However I have seen a few examples of other chunks, usually xml metadata, appearing after the 'data' chunk. This confuses some players.

For more information search for tech3285.pdf from the European Broadcasting Union website (tech.EBU.ch).

Upvotes: 1

Mark Heath
Mark Heath

Reputation: 49522

The JUNK chunk is reserved space to allow a BWF file to be converted into an RF64 file on the fly if the size goes over 4GB. The JUNK chunk is the same size as a ds64 chunk, and will be replaced with a ds64 chunk if the conversion to RF64 is needed. Read more about it here.

My reading of the BWF spec is that you have to have a bext chunk for it to be a BWF.

Upvotes: 2

guitarflow
guitarflow

Reputation: 2970

As far as I know, a broadcast wave file will have the 'bext' header extension. If a file does not have the 'bext' header extension, it will be a normal WAV/AIFF or whatever file.

Broadcast wave headers are used especially if you want to give a file more information about itself in the header which isn't to be seen immediately from its name. For playing back, this info isn't necessary to know. Just if you want to show or search the meta information somehow.

PCM isn't a file format. All files that handle uncompressed data are PCM files. Such as WAV/BWF, AIFF or SD2 for example. With encoded files like MP3 or AAC you get the raw PCM values after decoding.

Upvotes: 2

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