[FFmpeg-user] exponential decay, is it possible?

[Michael Koch]

I'd like to ask if it's possible to make an exponential decay effect 
with FFmpeg.
Let's assume a pixel is fashing to luminance = 1 in just one frame. Then 
in the output video I'd like to have the pixel flashing to 1 
immediately, followed by an exponential decay with a time constant of a 
few seconds.

The mathematics would be something like this:

luminance = 0.95 * luminance_in_last_frame;     // exponential decay
if (luminance_in_new_frame > luminance)
   luminance = luminance_in_new_frame;

Is there any trick to do this with already existing video filters?

Thanks,
Michael