On Fri, Mar 13, 2009 at 12:15:24PM -0700, Gary Kline wrote:
>       guys, this is for any compression experts on-list.  my main
>       desktop is nearly full.  i'm looking for the best means of
>       compressing [mostly] audio files.  mp3, ogg, and .flag.

All of these are already compressed. Trying to compress them further is
a waste of time. See below. You can make smaller mp3 or ogg vorbis files
by encoding them at a lower bitrate or quality setting.

I did a test on compression some time ago.

I started with a track ripped from CD by cdrecord. I used 'lame -V 2' to
convert to mp3, 'oggenc -q 5' to convert to ogg vorbis, and 'flac -6' to
convert to flac.

File sizes were (in kilobytes, using 'du -k'):
20256   track01.flac
4592    track01.mp3
3792    track01.ogg
37584   track01.wav

The mp3 and ogg files are small because they employ 'lossy'
compression. On the other hand, flac is lossless compression. I tried
several (obviously lossless) archivers.

First I compressed them all with 'gzip -9':
20240   track01.flac.gz
4560    track01.mp3.gz
3760    track01.ogg.gz
33840   track01.wav.gz

As you can see these sound files don't compress well. The first three
because they are already compressed, and the wav file probably because
the gzip algorightm isn't a good match for sound data.

Then I tried with 'bzip2 -9':
20336   track01.flac.bz2
4560    track01.mp3.bz2
3776    track01.ogg.bz2
32080   track01.wav.bz2

Next up is 'rzip -9':

20240   track01.flac.rz
4560    track01.mp3.rz
3776    track01.ogg.rz
32080   track01.wav.rz

And finally 7zip '7z a -mx=9':

20448   track01.flac.7z
4576    track01.mp3.7z
3760    track01.ogg.7z
31424   track01.wav.7z

My conclusions were:
- The general archivers can compress the wav somewhat without loss, but
  none do as well as the dedicated lossless compression program flac.
- Trying to compress mp3, ogg and flac files further is a waste of time.
- If you want smaller files, use lossy compression like mp3 or ogg
  vorbis, and pick the lowest quality level that sounds acceptable to you.

R.F.Smith                                   http://www.xs4all.nl/~rsmith/
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