[Flac-dev] Variable Bit Rate

Dennis Brunnenmeyer dennisb at chronometrics.com
Mon May 23 11:35:39 PDT 2011

I'm well aware how compression works. But images and document files do 
not depend on the relative timing of the data to reproduce themselves. 
They are in essence only two-dimensional in space, whereas the data in a 
sound file is time-dependent.

The question really has more to do with the decoded FLAC stream output, 
which I presume is a linear PCM file, e.g. WAV.  If FLAC is lossless and 
created from an original CBR WAV file, is is true that the decoded 
output is also CBR when played?

That is, WAV in = WAV out, where both are CBR?

Thanks for any insights on this matter. I've been told that because a 
FLAC stream from a server to an application is VBR, that certain 
transients are not handled correctly, like the ringing of bells. If this 
were true, FLAC would not be lossless in this application.


On 5/23/2011 10:58 AM, Masklinn wrote:
> On 2011-05-23, at 19:26 , Dennis Brunnenmeyer wrote:
>> Is FLAC a variable bit rate format when streamed? If so, how can it be truly lossless?
> The same way zip and PNG compression are truly lossless: something can take more space than the information it contains needs.
> For instance, take a 1024*1024 completely white bitmap. Your bitmap file is 1MB (1048576 bytes). A good PNG compressor can get it to 200 bytes (this is not a typo: I have a completely white 1024*1024 PNG file in 222 bytes).
> Well it's the same with sound (a 5mn track with no sound whatsoever contains less information than "Nun seh' ich wohl, warum so dunkle Flammen"). That's also why the format can't help but be VBR: different pieces of sound contain different amounts of information per second, and therefore have different compression ratio (and compression ratios can --- very rarely --- go above even 1: white noise is completely incompressible, when you add FLAC metadata you end up with a FLAC file bigger than the source WAV)


Dennis Brunnenmeyer
Director of Engineering
15019 Rattlesnake Road
Grass Valley, CA 95945-8710
Office:   1 (530) 477-9015
Mobile: 1 (530) 320-9025
eMail: dennisb /at/ chronometrics /dot/ com

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