CRf Values 17/18-Meaning ?

[rodling]

I have heard the claim that encoding at CRf values of 17/18 is the way to get the best quality, but is there any actual reasoning behind this ?

Since CRF values start at zero, is there any particular reason 17-18 is when you will get the best file size reduction with no quality loss, or is this just a subjective range that some people think is true.

[Sharc]

For x264 no quality loss would be CRF 0 (lossless). Any larger CRF introduces losses. For most people and typical sources CRF 17 .... 20 is a good compromise between compression (file size) and visual quality. It's subjective and source dependent.
Quality and file size depend on other encoder settings as well.

[rodling]

how much is CRF value of 0 usually going to reduce file size ?

[Sharc]

how much is CRF value of 0 usually going to reduce file size ?

It depends on the source. It usually blows up the filesize of already compressed sources (DVD, Blu-ray ....) but may reduce the size somewhat of uncompressed sources. Why don't you just try for your sources what you get for various CRF, and find the compromise which suits your personal preference?
And familiarize with the basics of video encoding and compression.
Simply put and assuming all other encoder parameters are the same:
- Lower CRF means less compression = higher file size with lower losses and less compression artifacts
- Higher CRF means more compression = smaller file size with more losses and more compression artifacts
Find your sweet spot. There is no "best".

[rodling]

I don't have a super high end computer and at least with handbrake encoding seems to take awhile, certainly
too long to just keep doing trial and error, but I guess I'll do it anyway.

[Sharc]

I don't have a super high end computer and at least with handbrake encoding seems to take awhile, certainly
too long to just keep doing trial and error, but I guess I'll do it anyway.

It is usually sufficient for testing to encode selected short snippets only (motion, rich of details, dark scene). You can't predict the filesize though.
If file size matters and you want to encode for a fixed filesize (bitrate) you need to do 2-pass encoding and set the bitrate. For the calculation of the bitrate take a look here:
https://forum.videohelp.com/threads/416495-Particle-outline-after-conversion#post2756854

[4kblurayguru]

is there any particular reason 17-18 is when you will get the best file size reduction with no quality loss,.

just a recommendation, not law, you can do 15 , 10 or 23 if you want

i use default crf for videos from my camcorder, i see no major difference from crf 18-23, other than file size. i focus on preset - slow or slower. I get 1fps with AVC and 0.01fps with vp9

[rodling]

is there any particular reason 17-18 is when you will get the best file size reduction with no quality loss,.

just a recommendation, not law, you can do 15 , 10 or 23 if you want

i use default crf for videos from my camcorder, i see no major difference from crf 18-23, other than file size. i focus on preset - slow or slower. I get 1fps with AVC and 0.01fps with vp9

I hope I read that wrong, the speed your computer encodes the video is 1fps or less ? are you trying to encode 4k on an old computer ? Whatever the case, I for sure would not bother with encoding at that speed.