[ogg-dev] ogg dirac granulepos in oggz tools

Silvia Pfeiffer silviapfeiffer1 at gmail.com
Fri Nov 21 19:14:55 PST 2008

On Sat, Nov 22, 2008 at 2:11 AM, Conrad Parker <conrad at metadecks.org> wrote:
> 2008/11/21 David Flynn <davidf+nntp at woaf.net>:
>> On 2008-11-21, Conrad Parker <conrad at metadecks.org> wrote:
>>> 2008/11/15 David Flynn <davidf+nntp at woaf.net>:
>>>> On 2008-11-14, Conrad Parker <conrad at metadecks.org> wrote:
> a granule is a frame, field, sample etc., and granulerate is framerate,
> samplerate etc.
>> [1] Mostly with regard to a hypothetical 'timeline' -- but these are
>> questions for some later time.
> Yeah; I've been thinking we should at least add a field to skeleton to
> accomodate the Dirac mapping. The main thing is to identify which algorithm
> to use for converting granulepos to time. Currently two are defined (linear
> like Vorbis PCM, or Theora's granuleshift). The granuleshift method works
> for many stream types with reverse dependencies, but cannot take into
> account streams that are not encoded in presentation order.
> The way the current Dirac mapping works doesn't really fit into either of
> those granulepos schemes, though it does do an awesomely clever job of
> allowing pt to be calculated with the Theora granuleshift method :-)

Fisbone packets are built in a way that new fields can be inserted
before the message header fields without breaking backwards
compatibility. I would support such an extension!

>> [2] http://wiki.xiph.org/index.php/Ogg_Skeleton says:
>>  """
>>    allowing to map a granule position to time by calculating
>>    "granulepos / granulerate"
>>  """
>> But that doesn't seem to be what happened in liboggz -- it used GPH+L.
> thanks for pointing that out, the wiki page is incorrect.

I don't understand enough about how it is wrong. Can you correct the wiki page?


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