Hello Michael,
sorry for the delay, i was out of the office for a conference.
On 12/03/2012 08:46 AM, Michael Raab wrote:
> our OpenSG-based application uses ffmpeg to encode captured image sequences
> to generate some nice videos. Since switching from an old libav version
> (2011) to the recent build we investigated some emtpy frames when capturing
> some camera movement.
> After some research on that found that whenever we got invalid/empty frames,
> the calculated/interpolated camera transformation was invalid (contained some
> -1.IND values in rotation section). After digging deeper the problem seems to
> be that in Quaternion.slerp() a call to sin() returns these -1.IND values.
> When animating the camera without capturing and encoding the frames
> afterwards everything seems to run fine. I already asked on the ffmpeg
> mailing list but they also seem to have no clue.
>
> Anyone who has an idea why sin() may return -1.IND for a valid input value?
unfortunately no; to be honest I'm not even sure what -1.IND is meant to
indicate, AFAIK float has +/-INF and quiet/signalling NaN as special
"not-really-a-number" values.
What is the input that produces such a value? Is it a very large value
and you are perhaps running into a precision problem in the sin()
implementation? In that case you could try mapping your input value to
[0, 2*PI] before passing it to sin().
Another thought: does ffmpeg modify rounding modes or the trapping state
of floating point operations? Not sure how that would cause something
relatively straightforward as sin() to stop working, but still...
Cheers,
Carsten
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