Hi Alex!
> 1) M/S stereo require both channels to switch block types simultaneously -
> why/how doesn't intensity? (I run intensity using long only for now.) The
> ISO decoder takes the block type for decoding the intensity position info
> >from the left channel, which essentially requires both channels to have the
> same block type, as there is no simple way to reconcile long and short
> scalefactor bands. So why aren't the channels required to have the same
> block type?
I think there is an implicit requirement to be of the same block type.
> 2) In layer-II coding, the first band to code using intensity is specified
> by the mode extension - in layer-III it can by dynamically varied and is
> understood implicitly from the bitstream by the decoder. But the spec gives
> no suggestions for algorithms on where to begin using intensity. (I used a
> fixed #define.) Does anyone have a reference on this? (Exhaustive search
> is not really an option?)
If I understand the DOCs right, then in IS mode, starting at
lower frequency bands, the last right channel scalefactor band
not completely zero marks the last MS or LR coded band. All bands
above are intensity stereo coded, magnitudes in left channel,
position in right channel. Bands with illegal intensity position
have to be MS or LR decoded.
note: the zero part of the spectrum goes from bigvalues*2+count1*4
So you will have to calculate the corresponding scalefactor
band.
Ciao Robert
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