[Vorbis] Split an audio in more part and recreate the original

[Lorenzo]

Hi all,
I would like to split an audio stream into more encoded flows (for 
example 1, 2 and 3) that have these features:
1)  The flows  must be re-assemblable and must generate the original 
stream (1+2+3 = original stream)
2)  I can listen only the flow number 1 (even if the audio quality is 
worst than the original, of course)
3)  I can listen only the flows number 1 and 2 (the quality of the audio 
is better than if I've got only the flow number 1, but worst than if 
I've got all the three flows)
4) Each flow use less bandwidth than the original flow (otherwise is 
useless!)

It is like TV that broadcast black&white information and colours. We can 
view only B&W , or we can view also the colors.

Vorbis can help me to do this? How hard is it?

Thank you,


LB