[vorbis-dev] Packet Granule position

[Sebastian Gesemann]

Hi Adriano !

On Fri, 26 Mar 2004, Adriano Almeida wrote:

> Is there a way to know the exact packet granule position before I decode it?
> is there any relationship between packet size and granule position? I know
> each page has its own granule position, can i calculate it for each packet??

I'm not sure what you mean by "packet granule position". A packet
contains several audio samples, so it has a granule pos start end
granule pos end (actually it's a bit more complicated because of
the overlap-add synthesis).

According to the "Ogg logical bitstream framing" specification the
granule pos of a page determines the position after the last packet
that finishes on that page (or -1 if no packet finishes on that
page).

According to "Ogg Vorbis I format specification: codec setup and
packet decode" each audio packet starts with a zero-bit followed
by a "mode" field. Dependent on the mode's "blockflag" the packet
stores either 0.5*blocksize_0 or 0.5*blocksize_1 samples per
channel.

HTH,
Sebastian


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