[Flac] flac -- exhaustive model search vs. -A <*>?

[Linda Walsh]

Martin Leese wrote:
>
> At:
> http://flac.sourceforge.net/documentation_tools_flac.html#flac_options_exhaustive_model_search
>
> it states, "If the max LPC order is high this
> can significantly increase the encode time."
> This suggest that if the max LPC order is low
> then using -e will not be slow.
>   
----
    That brings up another question then... What is 'hi' (v. low?)...

The doc on -l makes it look like 12 is the max for "subset streams":

          -l #, --max-lpc-order=#
              Specifies the maximum LPC order. This number must be <= 
32.  For
              Subset  streams,  it must be <=12 if the sample rate is 
<=48kHz.
              If 0, the encoder will not attempt  generic  linear  
prediction,
              and  use only fixed predictors. Using fixed predictors is 
faster
              but usually results in files being 5-10% larger.
---
What's a subset stream?  Under "--lax", it says:
    --lax  Allow  encoder to generate non-Subset files.  The resulting FLAC
              file may not be streamable or might have trouble being 
played in
              all  players  (especially  hardware devices), so you 
should only
              use this option in  combination  with  custom  encoding  
options
              meant for archival.
===
There -- it sounds like  "subset" refers to the subset of "flac encodings"
that is "streamable" and/or work on all(or most) players...  Sorta like
320Kbps being the max rate for "MP3's that conform to the standard"... 

If that's the case then the highest -l value one can 'portably' use would
be 12?  FWIW, I've tried 16 & 12 and noticed no difference in exhaustive's
execution time.

Another "nit" I noticed, from 
http://flac.sourceforge.net/documentation_format_overview.html
in the inter-channel-decorrelation section -- it mentions -m vs.
-M, where -m always uses mid+side channel whether it is bigger or not,
while -M adaptively uses mid+side or stereo depending on which is better.

Why would flac levels 7 and 8 use -m (always when -M allows adaptive 
encoding
based on which is better?






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