[theora-dev] How to get the duration of a file or track?

Conrad Parker conrad at metadecks.org
Mon Aug 27 21:47:40 PDT 2007

On 28/08/07, Shane Stephens <shane.stephens at gmail.com> wrote:
> Please note that oggzinfo actually passes right through the file twice in
> order to gather these statistics - this is not necessary if you simply want
> to determine the Content-Duration.  I'm also not 100% sure whether liboggz
> correctly supports chained oggs.

liboggz doesn't make any attempt to handle chaining -- for normal
reading, it simply calls page/packet callbacks as it sees them.

Consequently, oggzinfo will report info for the bitstreams in each
chain of a file, but does not take chains into account. As a result it
gets the duration and bitrates for chained files wrong.

liboggz and oggz-tools need at least the following to handle chained files:

 - seeking should take chains into account
 - reading should report chain boundaries (eg. a "new chain" callback)
 - writing should allow writing of chains (currently you would
basically need to create a new OGGZ* writer for each chain, attached
to the same fd)
 - oggzinfo should calculate duration for each chain, sum durations
for the whole file, and use per-chain duration for bitrate calculation


 - oggz-validate, oggzrip, oggzdump, oggzdiff already handle chained files ok
 - oggz-scan handles chained files, but reports scene-change times
relative to chain start
 - oggzmerge: it would be non-trivial to merge chained files unless
the chain durations matched.



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