[Flac-dev] ogg-flac?

[Josh Coalson]

--- Matt Zimmerman <mdz at debian.org> wrote:
> On Mon, Mar 26, 2001 at 11:34:04AM -0800, Josh Coalson wrote:
> 
> > --- "smoerk at gmx.de" <smoerk at gmx.de> wrote:
> > > hi,
> > > 
> > > would it be possible to use ogg as container for flac? so you
> could use all
> > > the features of the ogg format.
> > >
> > A long time back I looked into that but couldn't find a detailed
> enough spec.
> > I plan on taking a look again when I get a chance.
> > 
> > Monty has plans to revive Squish but he's a busy guy and may not
> get around
> > to it for a while.  Also, almost all codecs I tested beat Squish
> '98 so the
> > bar is a little higher nowadays.
> > 
> > If FLAC fits into Ogg and the Ogg group is willing, I'm all for it.
> 
> I had been thinking about this as well, and from looking at the API,
> it seems
> that the ogg format doesn't care much at all about what it's
> streaming; it's
> treated as a sequence of random bytes, divided into pages.  The
> encoding
> process, as documented in libogg, is approximately:
> 
>   * Use the encoding engine to produce a raw packet of data.
>   * Call ogg_stream_packetin to submit a raw packet to the stream.
>   * Use ogg_stream_pageout to output a page, if enough data has been
> submitted.
>     Otherwise, continue submitting data.
> 
> The documentation is much improved.  However, if the existing FLAC
> format were
> encapsulated by Ogg, there would be a lot of duplicate data
> (specifically,
> framing, synchronization, error detection, etc.).  Ogg also has a
> facility for
> interleaving multiple channels, though I'm not sure whether FLAC
> operates on
> each channel individually (does it?).
> 
In FLAC the framing and synchronization is not done at the
individual channel level.  If such is done in Ogg I'm not
sure how they take advantage of interchannel correlation
unless maybe a stereo channel is treated as one 'super-
channel'.  In this case, a FLAC stream could, like you said,
be treated as one super-channel and encapsulated.  FLAC's
framing overhead is pretty small, usually 6-10 bytes per frame.

Josh


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