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List:       theora
Subject:    Re: [theora] OGGZ Seeking in Theora
From:       Stefan Weber <s_weber () blyth ! ch>
Date:       2010-06-29 13:09:35
Message-ID: 4C29F08F.9050804 () blyth ! ch
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Chris,

Thanks a bunch, that's probably the best approach for now.

Regards,
Stefan

Am 28.06.2010 16:09, schrieb chris@pearce.org.nz:
> On Mon 28/06/10  7:57 PM , Stefan Weber s_weber@blyth.ch sent:
> 
> > I'd really like to implement a correct seeking functionality.
> > 
> A quick hack to get visual artifact free seeking with liboggz is to seek to a time \
> which should lie before a keyframe prior to your seek target, and then decode \
> forwards to the target frame. This will mean seeking takes a few more MS (since \
> you'll likely be decoding more than required), but it's better than visual \
> artifacts after seeking, and is easy to implement to get seeking working. 
> We can calculate the maximum time between frames as:
> 
> max_keyframe_interval_ms = ((1<<  th_info.keyframe_granule_shift) - 1) * \
> th_info.fps_denominator / th_info.fps_numerator 
> So seek to max_keyframe_interval_ms before your target and pump the decode until \
> you reach the target frame. You may need to subtract a few extra milliseconds in \
> there if you're not using the seek-rewrite branch of liboggz to work around old \
> edge-edge case bugs. 
> 
> All the best,
> Chris P.
> 
> 
> 
> 
> > Whats the best method to get the time representation of a frame?
> > Regards,
> > Stefan
> > Am 21.06.2010 11:58, schrieb Stefan Weber:    Dear all
> > Conrad, thank you for your inputs and your help so far. I will use
> > and test the seek-rewrite branch as soon as possible.
> > I figured out that the Keyframe position in the granulepos is the
> > NUMBER of the keyframe. When seeking with OGGZ, one has to supply the
> > TIME-position (milliseconds) of the desired frame. So I made a short
> > workaround by calculating the milliseconds position as follows:
> > ms = (granulepos>>  shift) * 1000 / noFPS;
> > Needless to say, this won't point me to the exact keyframe
> > position. Probably this rough calculation is not exact enough?
> > What is the best approach to calculate the TIME-position for
> > oggz-seeking out of a given frame number?
> > Kind regards,
> > Stefan
> > 
> > 
> > 
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