pp7[=qp[:mode]]
Variant of the spp filter, similar to spp=6 with 7 point DCT
where only the center sample is used after IDCT.
<qp>
Force quantization parameter (default: 0, use QP from
video).
<mode>
0: hard thresholding
1: soft thresholding (better deringing, but blurrier)
2: medium thresholding (default, good results)