[Flac-dev] FLAC: compression ratio

[Brian Willoughby]

Harry,

This question belongs on the general [FLAC] list, not the developer  
list.  The topic would only become a developer issue after it was  
determined that a change in the code would be useful and/or possible.

That said, FLAC is already capable of reaching 50% or 40% of the  
original.  I have seen FLAC reach 30% (ratio = 0.3x) or even less  
with my files.  It depends upon the content because FLAC keeps all  
the content.  Other compression formats which are lossy can choose  
almost any ratio, because they are throwing away information, and you  
can always throw away more.  FLAC cannot choose the ratio because it  
is keeping all the information, and it must not throw anything away.   
The less there is, the lower the ratio.

To put it another way, overly "produced" music will compress less,  
while raw recordings of live an natural sounds will compress more.   
If you're always seeing 60%, then your CD tracks are probably not  
classical or highly-dynamic live jazz music.  Death metal white noise  
music will probably only compress to about 90% or 80%.

Brian Willoughby
Sound Consulting

P.S.  You should carefully study the online FAQ at http:// 
flac.sourceforge.net/faq.html#general__lowest_bitrate
because it holds the answer to your question.  It mentions that  
ratios from 100% to 0% are possible, depending upon the track.  e.g.

What is the lowest bitrate (or highest compression) achievable with  
FLAC?

With FLAC you do not specify a bitrate like with some lossy codecs.  
It's more like specifying a quality with Vorbis or MPC, except with  
FLAC the quality is always "lossless" and the resulting bitrate is  
roughly proportional to the amount of information in the original  
signal. You cannot control the bitrate much and the result can be  
from around 100% of the input rate (if you are encoding noise), down  
to almost 0 (encoding silence).


On Aug 27, 2007, at 04:50, Harry Sack wrote:

hi flac-dev list!

I see, when compressing CD-audio tracks, I can reach up to 60% (ratio  
= 0.6x) of the original WAV file after compression. I was wondering  
if the FLAC codec could become as good as reaching 50% of the  
original WAV file in the future or if we are already at the (almost)  
maximum compression possible?

thx