X264 CRF source related?

[axel__17]

Hi all
I am trying to better understand CRF encodings and I have a dumb question which I didn't find it an answer (yet):
almost everyone suggests to have a CRF value higher for HD content (e.g. 22) with respect of DVD (e.g. 20), but why?

I would have expected the opposite:
since CRF targets quality rate it seems like I am wasting more quality (with a higher CRF value) for higher quality source (BD) compared to DVD.

Any hint is more than welcome

Regards
A

[nm]

almost everyone suggests to have a CRF value higher for HD content (e.g. 22) with respect of DVD (e.g. 20), but why?

I think the actual reason for that suggestion is that you'll be watching both the HD and the SD encodes on the same display. SD gets upscaled, which makes encoding artifacts more annoying and therefore compensating with a lower CRF may be a good idea.

[nixo]

Also, for the same reason, I think it makes some sense to encode 16:9 SD material at a slightly lower CRF value than 4:3 SD material. Unless, of course, you happen to use a 4:3 display in which case the opposite would be true.

--
Nikolaj

[axel__17]

Let's put it simpler...

If I rip from the same source (Blu-ray) but make different resolution (480p, 720p, 1080p)
does it still make sense to have a higher CRF for the 480p compared to the 720p and 1080p?

I used to Rip DVD at RF 20 but I'm switching to BD and I wonder if it makes any sense to
differentiate between the 480p rip and the hd rip.

Thnx
A

[nm]

Let's put it simpler...

If I rip from the same source (Blu-ray) but make different resolution (480p, 720p, 1080p)
does it still make sense to have a higher CRF for the 480p compared to the 720p and 1080p?

Lower CRF value for 480p makes sense if you intend to watch everything at the same display size. If you are happy with CRF 20 for 480p, CRF 21 is probably ok for 720p and CRF 22 for 1080p.

[nibus]

Run some test encodes at incrementing crf values and watch them on your display at a normal distance, and when you start seeing noticeable artifacts, just bump it down 1 crf and go with that. It really depends on your display - on some displays you can't tell the difference between 18 and 22. On others its obvious.

[GEfS]

I'm not using CRF but I think 17-24 is ok for HD.
I don't use CRF and I can't give a advise for SD.