[ogg-dev] Fwd: Additional ogg audio fomats (speex, flac, PCM)

[Timothy B. Terriberry]

clancy hood wrote:
> [Woops, forgot to reply to the list ; just sent the following to Ralph]

No worries, I've been doing this for years and I still managed to send 
you my reply off-list. I hate that particular configuration of our lists.

> 1) It seems I can always rely on the first byte of the first vorbis
> comment page to be 3. Is this right?
> I see that some pages begin with a byte and then "vorbis", but haven't
> yet found a resource that tells me what that byte means.

This is explained in the Vorbis spec: 
http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html#x1-610004.2.1

> 2) In fact, must page 2 of an ogg be a comment page, or may it be
> missing altogether? So far, I've found "empty" pages with a single page
> segment, but never a missing comment page.

The second packet of a Vorbis stream must always be a comment header. It 
isn't legal to omit it. It can span multiple pages (and will sometimes 
do so when people embed album art in it).