[Flac-users] Re: [Flac-dev] What is "mid-side coding"?

[Curt Sampson]

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