[Vorbis-dev] How to convert multichannel to mono/stereo?

[tut.by]

Sorry for the questions out of the mail list's subject.

1)

Could you help me with getting information on how
can I convert multichannecl (e.g. 5.1) non-encoded
(PCM) data into mono\stereo? I suppose this performed in
the manner like:
Left = x1*(Front Left)+x2*(Back Left)....
But is there exist commonly used standards to perform this task?

2)

It seems FLAC pjoject have been frozen for some time.
E.g. recent bugs reported in 
http://sourceforge.net/tracker/?group_id=13478&atid=113478
are without answers.
May be somebody know reasons of this?

Thanks in advance, Vitaly (nvit at tut.by).