[vorbis-dev] application/ogg is a proposed Internet standard.

Beni Cherniavsky cben at techunix.technion.ac.il
Tue Feb 4 13:31:19 PST 2003

On 2003-02-04, Ralph Giles wrote:

> On Monday, February 3, 2003, at 10:07  pm, Beni Cherniavsky wrote:
> > How are keyframes fundamentally different from binary seeking?  You
> > still need to find the keyframe start, don't you?  It's just an
> > obvious optimization that for small enough distances you read
> > sequentially forward instead of doing the binary search up to the
> > exact byte.  It's just like Ogg seeking with one packet for each
> > key+differences block.
> Right. I think Segher has not been convincing here. He does have a
> point about long-latency access, but the only way I see a jump table
> being helpful is an external chapter pointer file, a la DVD video. If
> you're going to have pointers, that can include byte offsets as easily
> as time offsets. That's a different class of problem from seeking
> because the table is short.
My point was that keyframes are not relevant - they are seeking
restriction, not a solution.  Segher's point that TOC / jump tables can
improve seeking effeciency still holds.

> >> For quite a few applications, synchronizing everything to some 48kHz
> >> or 44.1kHz audio clock may be good enough, and that is of course the
> >> prefered way to tie a video stream to an audio stream for playback,
> >> but
> >> it certainly is not the correct solution for all applications.
> Right, it's nice, but it's the player's job (or the demux library's)
> precisely because of the 'quite a few applications' part.
I can see many tools that will want to process a stream without decoding
it: de/mux, cutter, anything that displays metadata (length), etc.

Perhaps it would be useful to define a middle "meta-codec" (for lack of
better name) layer.  It would have lightweight duties - recognize the
stream type, convert granulepos<->time, perhaps extract metadata.

The idea is that several codecs (e.g. vorbis, speex, etc.) can share one
meta-codec.  This allows generic application to wwritten against a small
library that doesn't even need to change for new codecs if they are
compatible on the meta-codec level.  Still, if the need arise, you can
introduce completely new meta-codecs so no a-priori limitations are set on
the possible formats.

Beni Cherniavsky <cben at tx.technion.ac.il>

If somebody builds a time machine he can gateway the Internet to itself
with a time offset.  I wonder what implications that would have...
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