[ogg-dev] [Schrodinger-devel] ogg dirac granulepos in oggz tools

Ralph Giles giles at xiph.org
Thu Nov 13 15:08:59 PST 2008

On Thu, Nov 13, 2008 at 2:54 PM, David Flynn <davidf+nntp at woaf.net> wrote:

> The only niggle i have with this file is that the EOS page has a bizare
> timestamp.  imho, because there is no picture in the eos page, there is
> no meaningful time for it, so the granulepos should be -1 on the eos
> page on the dirac logical stream.

ds and I talked about this a bit yesterday. The rfc says the special
value of 0xFFFFFFFFFFFFFFFF "indicates that no packets finish on that
page." So it's a bit misleading to say this. Moreover, it's convenient
for duration calculation (and scanning backward) if the final page has
a granulepos. With other mappings, when considering a non-frame eos
page, we've generally concluded it's better that it carry the same
granulepos as the last frame.

In this case, the page has a packet, and while that packet affects
decoder state, it doesn't itself advance production of decodeable
output, so it make some sense for it to have presentation timestamp
the same as the last decodable frame in the stream, and perhaps a
decode timestamp likewise the same. Does this not make sense in the
dirac granulepos encoding?


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