spp[=quality[:qp[:mode]]]
Simple postprocessing filter that compresses and decompresses
the image at several (or - in the case of quality level 6 - all)
shifts and averages the results.
<quality>
0-6 (default: 3)
<qp>
Force quantization parameter (default: 0, use QP from
video).
<mode>
0: hard thresholding (default)
1: soft thresholding (better deringing, but blurrier)
4: like 0, but also use B-frames' QP (may cause flicker)
5: like 1, but also use B-frames' QP (may cause flicker)