Question about x264 deblock and psy-rd

[simps]

Filters like convolution3d and Smart Smoother High Quality do a good job increasing the compressibility.

I am not sure what deblock and psy-rd do exactly, but by tunning those settings in a smart way, its possible to get a similar effect.

So, should I still use filters like convolution3d and Smart Smoother High Quality when I need to encode with very low bitrates in x264, or the deblock and psy-rd functions will do the job better?

[nurbs]

The inloop deblocker in H.264 isn't an alternative to preprocessing. It's there to keep blocking artifacts created by compressing the video in check and to make prediction easier. Psy-Rd generally makes the picture look sharper by picking a less accurate but better looking representation for a block.

[LoRd_MuldeR]

Psy-Rd generally makes the picture look sharper by picking a less accurate but better looking representation for a block.

Well, "less accurate" in the sense of PSNR, but more accurate in the sense of the perception of a human viewer :cool:


I am not sure what deblock and psy-rd do exactly, but by tunning those settings in a smart way, its possible to get a similar effect.

H.264's In-Loop Deblocking exists to suppress "blocking" artifacts.

It works more effective than a post-processing filters, because it works already during the encoding process, which means that P- and B-Frames refer to the already deblocked frames.

Also it works adaptive, which means that the deblocking strength is adapted to the amount of blocking introduced by the H.264 compression.

Most important H.264's Deblocking filter can NOT replace a pre-processing filter, because it does NOT try to remove "blocking" artifacts that were already present in your source at all!

(For decent bit-rates I would suggest to try lowering the H.264 Deblocking a bit, like -1:-1. Anyway, it's almost always a bad idea to disable the In-Loop Deblocking).


Rule of thumb for tuning Psy-RD strength:

The higher you raise the Psy-RD strength, the more sharpness and fine detail (like grain) can be retained. But with stronger Psy-RD also the danger for undesired artifacts increases!

So it's all about finding the sweet-spot! And the x264 defaults, Psy-RD strength 1.0 for "Film" and strength 0.4 for "Animation" should be a good starting point ;)

[Blue_MiSfit]

Good descriptions so far.

Just remember that the denoising filters you mentioned are just that - denoising filters. They alter the source video to either improve compressibility or to meet a certain aesthetic.

Adjusting deblocking and Psy-RD settings alter the behavior of the encoder to favor subjective quality versus objective quality.

Also keep in mind that the defaults implied by --tune film do a very good job 99% of the time, and it's not usually necessary to tweak them.

Derek