avfilter/vf_idet: add a "half_life" option for statistics

This can be useful for videos in which the interlacing pattern changes.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/vf_idet: fix rounding of av_dict_set_fxp()

fixes the remainder overflowing beyond .999

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/vf_idet: use av_rescale()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/vf_idet: use exp2()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>