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List:       kde-multimedia
Subject:    Optimized mp3
From:       Stefan Westerfeld <stefan () space ! twc ! de>
Date:       2000-11-28 14:16:26
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   Hi!

On Sat, Nov 25, 2000 at 05:23:42PM -0800, Charles Samuels wrote:
> Let's put it this way:
> I ran winders95 on a P133.  I play MP3s just fine.  I switched to linux, and 
> kmp3 could play MP3s file.  Now I use a dual P2/300, and I don't mind a media 
> player that takes 20% of my entire computer (that's 40% of a P2/300)

I've done some optimizations in the last two days. MP3 playing is now 50%
faster than it used to be (code is in the CVS). What I did was this:

 * inline Mpegtoraw::putraw
 * inline Mpegtoraw::get1bit/getbits9
 * use a table, to make huffman decoding a simple table lookup in most cases
 * avoid float -> int -> float conversions for mp3 decoding
 * resample only if necessary (i.e. don't if artsd and the mp3 are 44100 Hz)    

Overall this means, that KDE2.1 will perform significantly better than
KDE2.0. Besides the above mpeglib optimizations, artsd has evolved over
the post-2.0 period, too.


Still, playing an mp3 with artsd and mpeglib is slower than playing it purely
with a standalone player. I have tested it with a stripped down version of
splay that plays a certain mp3 in 11 seconds, whereas rendering it with
mpeglib/aRts takes 16 seconds.

Where we loose these additional 5 seconds, I can not say. Some things to
try might be

 - improve the interface between aRts and mpeglib
 - improve the aRts flowsystem
 - improve the mp3 decompression itself
 - write a new mp3 PlayObject which is unthreaded and does not use mpeglib

It is a lot easier to do benchmarks with the new program "playtofile" which
I've put into the CVS (kdelibs/arts/examples) than it is without (you need to
compile mpeglib without defining PTHREADEDMPEG). It allows you to look how
long decompressing a file takes if you do it as fast as possible, which gives
a good base for benchmarking the threaded code.

If anybody is interested in looking into this further, please go ahead. I
can give you the code of the stripped down splay version I used for testing
(one possibility might be turning that into a PlayObject).

   Cu... Stefan
-- 
  -* Stefan Westerfeld, stefan@space.twc.de (PGP!), Hamburg/Germany
     KDE Developer, project infos at http://space.twc.de/~stefan/kde *-         
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