[Vorbis-dev] Ogg Pages Play Time?

[Michael Smith]

On 6/30/05, Horacio Sanson <hsanson at moegi.waseda.jp> wrote:
> 
> Are all audio pages in a Ogg/Vorbis stream the same size? do they have the
> same playback duration?

No. They will typically vary greatly in both size and duration.


> 
> I am developing a P2P streaming application where each client has to dowload
> the Ogg/Vorbis pages from other clients (peers) but I need to know how much
> time I have to download the next Ogg/Vorbis page before the playback reaches
> it.

The granulepos values in the ogg page headers will allow you to
calculate the duration of a particular page.

> 
> Something like
> 
> numCurrPages = Total of Ogg Pages already downloaded
> timePerPage     = Playback duration of one Page
> curPagePlaying = Current Ogg Page being decoded and played
> nextPage                = numCurrPages + 1
> 
> download nextPage before (numCurrPages - curPagePlaying)*timePerPage

You'll have to do a more complex calculation:

download next page before (granulepos of last page already present -
granulepos of currently playing sample)/sampling frequency.

This isn't greatly more difficult, though... You'll note that in this,
the total number of pages, and the size of each page, is totally
irrelevant.

Mike