flac dev - Sep 2004 - [Flac-users] What is "mid-side coding"?

Hi all!  I've just gotten into the FLAC world, and have read most of the 
documentation.  I have a question:  Mike Wren's frontend, upon looking at 
the DOS command line it automatically generates, uses the "-m" 
command.  This is for "mid-side coding for each frame".  What is 
this?  Specifically, is this like the mid-side recording technique?  If so, 
that means the audio file is being changed by flac, yes?  An explanation of 
"mid-side coding" would be most appreciated.

Thanks in advance,

Matt

On Thu, 15 Apr 2004, Dr. Nick wrote:
> This is for "mid-side coding for each frame".  What is
> this?  Specifically, is this like the mid-side recording technique?
Yes. The sum of the left and right channels is stored as the first
channel, and the difference as the second channel. If there's not a
lot of stereo information in the mix, this can result in a smaller,
more easily compressable second channel. (In the case where there's no
stereo information, the side channel will have nothing in it, which is
obviously very easy to compress.)
> If so, that means the audio file is being changed by flac, yes?
Well, yes; flac has to change the data in order to compress it;
unchanged data would not be compressed!

Or do you mean the decoded output of such a file would be different from
the original input? If so, no; the decoder will automatically convert
mid-side back into stereo if that's necessary.

cjs
-- 
Curt Sampson  <cjs@cynic.net>   +81 90 7737 2974   http://www.NetBSD.org
    Don't you know, in this new Dark Age, we're all light.  --XTC