Decoding starting from the middle of speex stream

Hi all,

I'm trying to decode only particular packets from the complete speex
stream (say I want to
decode speech from 2s to 5s from 10s stream). I use modified version
of speexenc.c
sample code provided in the documentation. However, first few packets decode to
corrupted samples. Decoding few packets before the part I'm interested
in doesn't help.

Is it possible at all to read only part of the stream and get valid
speech or I really need to
decode complete stream?

Thanks,
Slawek