Files getting bigger not smaller; why?

[dev84]

Hello

From what i understand and read on the net, when encoding video with x256 CRF and slower presets the encoder should try to compress more the video while maintaining the same visual quality.
Every file i test with slower presets i get bigger files than with faster presets.
Don't understand this, can some explain this to me?

Test file bit rate : 51.0 Mb/s
x256 crf20 preset medium bit rate : 5 658 kb/s
x256 crf20 preset slow bit rate : 6 548 kb/s

x265 3.0+1-ed72af837053

Thx
Pawel

[Blue_MiSfit]

The CRF scale is only equivalent with identical settings.

Pick a CRF at a given speed preset that gives you the quality you want. It's likely that if you experimented a bit here and found which CRF for the `slow` preset gave you very similar average bitrate to CRF 20 on `medium`, you'd have higher quality with the former. You'd also have more room to use an even higher CRF to reduce bitrate even further while maintaining equivalent quality.

[dev84]

Thank You, i always thought presets only change compression trying to maintain the same quality.
So, slower presets not only will compress better but will give better image quality.

I did a crf20 preset placebo now and it's bit rate is 6 681 kb/s, so it's not that much more than slow.
I see less obvious artifacts around edges in placebo than in medium at the same crf setting.
I guess the additional encoding time is worth it.

Thx again.

[benwaggoner]

Thank You, i always thought presets only change compression trying to maintain the same quality.
So, slower presets not only will compress better but will give better image quality.

I did a crf20 preset placebo now and it's bit rate is 6 681 kb/s, so it's not that much more than slow.
I see less obvious artifacts around edges in placebo than in medium at the same crf setting.
I guess the additional encoding time is worth it.
Slower settings will almost always increase quality at a given bitrate. But with CRF, sometimes it'll raise BOTH. For true apples-to-apples comparison, you should use 2-pass VBR to see what looks better at the same bitrate.

On net, you are likely to find that you can use a higher CRF value with slower settings, to wind up with better quality at the same overall ABR. But some encodes might still wind up bigger and some smaller than with faster presets.

[dev84]

Roger that, thank You