theora dev - Feb 2008 - dynamic change video quality........

I am going to change video quality parameter frame by frame. So i find a
parameter called* thisframequalityvalue* for this task. so i changed *cpi->
Configuration.ActiveMaxQ*(set "1" for half of the frames and set
"63" for
other half of frames)* *manually to change *thisframequalityvalue *parameter
in *UpdateFrame *frame function. But quality was not changed. Why is
that..Please help me to achieve my task....

-- 
Asanka Dilruk
Department of Computer Science and Eng.
University of Moratuwa....
http://www.asankadilruk.blogspot.com/
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On Feb 19, 2008 1:06 AM, Asanka Dilruk <adilruk@gmail.com>
wrote:
> I am going to change video quality parameter frame by frame.
There is currently no way to do this as there's no API.  You'd have to
reach directly into the internal code (which is, of course, what you
are suggesting), but this will be unstable.  Eg, once the Thusnelda
changes are merged back to mainline, this strategy will break.  The
symbols will not even be exposed in normal lib builds. Also, for what
you've described, you want to be influencing the bitrate management
parameters, not the quality parameter.

Anyway, I can see the use of this functionality, so I will see to
adding it to the API.  Derf, do you have documentation of your new API
so that I can do this correctly...?
> So i find a
> parameter called thisframequalityvalue for this task. so i changed
> cpi->Configuration.ActiveMaxQ(set "1" for half of the frames
and set "63"
> for other half of frames) manually to change thisframequalityvalue
parameter
> in UpdateFrame frame function. But quality was not changed. Why is
> that..
Because that's an internally computed value, and it is recomputed for
each frame internally regardless of what you set it to outside.  All
you're doing is accidentally clobbering the value of
LastFrameQualityValue, which will cause the internal regulation to go
haywire.  I'm not sure why you'd think that would do what you want...

Monty

xiphmont@xiph.org wrote:
> Anyway, I can see the use of this functionality, so I will see to
> adding it to the API.  Derf, do you have documentation of your new API
> so that I can do this correctly...?
The API was never really finished, or implemented, but you can get the
basic idea by looking at
http://people.xiph.org/~tterribe/doc/libtheora-exp/theoraenc_8h.html#encctlcodes
(see specifically TH_ENCCTL_SETUP_VBR and TH_ENCCTL_SETUP_CQI). The idea
was that these functions could be called at any point during the
encoding process to change the current encoding mode and parameters. A
TH_ENCCTL_SETUP_ABR was planned for an average bitrate mode, exposing
things like rate-control buffer size, etc.