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Comparing x264 “RF” settings in Handbrake (examples)

Here, I’m taking a look at various RF settings in Handbrake, both in terms of visuals and filesize.

 

I started with encodes from the “24” DVD (Season 6, Episode 1). If you have the same DVD and are looking to reproduce this test, the following settings were used:

  • x264 Preset: very slow
  • x264 Tune: none
  • x264 Profile: high
  • x264 Level: 4.1
  • Strict Anamorphic
  • Defaults for everything else (Handbrake 0.9.9 on OSX)

I tested the following RF values (listed in Handbrake under “Constant Quality”:
0, 10, 18, 20, 22, 24, 26, 28, 30, 32

 

VISUAL COMPARISON

I’ll start with a few screenshots at different RF values. There’s a video below too, but it comes with a bit of a caveat so might not show everything well for you. Pictures should work for nearly everyone. Note that the first one (RF0) is for reference (lossless).

x264 Handbrake encode at RF 0 x264 Handbrake encode at RF 10 x264 Handbrake encode at RF 18 x264 Handbrake encode at RF 20 x264 Handbrake encode at RF 22 x264 Handbrake encode at RF 24 x264 Handbrake encode at RF 26 x264 Handbrake encode at RF 28 x264 Handbrake encode at RF 30 x264 Handbrake encode at RF 32
(click for larger images)

 

Worth noting that x264’s psychovisual enhancements (trellis, etc) do a pretty good job of keeping detail where you’d notice it (the face), at the expense of the stuff you normally wouldn’t notice while watching (like those background areas). Of course, this only goes so far – once the RF value is high enough, there’s no saving Jack’s facial features from the effects of compression!

For those interested, I’ve also got another page on this site that lets you compare x264 vs x265 vs VP8 vs VP9 (at various RF and bitrate settings).

A static image isn’t always great, so here’s the 35-second video showcasing the difference between these RF settings in “24”. Note that you must click the appropriate buttons to watch this at full-screen 1080p if you want to see the differences somewhat clearly:

Note that YouTube re-compresses videos – I kept it at full-quality as long as I could, but I suspect YouTube won’t be fine with serving up a 360MB video that only lasts 35 seconds, so we’re at the mercy of their encoder.

FILE SIZE COMPARISON:

 

Now that you hopefully have an idea as to how each of the videos look, let’s see what each weighed in at for the full 43m8s episode. Note that these sizes ONLY apply to this episode of this source :

 

RF:0 – 6127.2MB (yes, 6.1GB)
RF:10 – 1925.2MB (yes, 1.9GB)
RF:18 – 355.6MB
RF:20 – 254.6MB
RF:22 – 197.3MB
RF:24 – 160.4MB
RF:26 – 136.1MB
RF:28 – 119.6MB
RF:30 – 107.5MB
RF:32 – 98.3MB

 

 

THE TAKEAWAY

 

A few things you probably observed when comparing to RF:0 (the lossless version):

  • RF10 looks almost identical to RF0 in the images, but still results in a massive file size – quite possibly similar to the size of your source. At that point, you’re probably better off keeping your original source rather than trying to recode it.
  • RF18-20 are incredibly close in the images, and it’s pretty hard to tell the difference when it comes to watching the video. The reductions in file size here tend to be substantial though, almost 100MB smaller (28% savings) by going from RF18 to RF20.
  • RF22-24 is about the point where visual differences are starting to become noticeable, but typically not to the point where they’d stand out when you’re actually watching. You save under 40MB (19%) by dropping from RF22 to RF24 here.
  • RF26-32 is where noticeable degradation comes about. It’s a matter of how much you can tolerate at this point. You really start to lose a lot of quality for each bit of filesize you try saving. Dropping the RF value by 2 saves under 20MB (9-12%), and the video is noticeably worse.

All that said, be sure to draw your own conclusions. And if you’re new to encoding with Handbrake, hopefully this has helped you to get a better understanding of the Constant Quality setting and the effects of various RF values.

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34 Comments on "Comparing x264 “RF” settings in Handbrake (examples)"

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Thank you so much for this. I installed linux on my encoding machine. Turns out my gig per 30 minutes was a bit over the top.
Taking your images to compare them via photoshop was very interesting as well.
Like: Make to layers RF18 and RF 20 and keep on as normal and divide that through the other. It shows pretty well how much bits have changed where.

Looks like this.
Quite enlightening. comment image

Jakewwa

Noticeable difference in contrast between RF18 and RF20 when zoomed in.

Devvrat Shukla

thank for this experiment bro 😉

jl

Good job man!

victor

Thanks Matt, as a newcomer to this stuff, that was very helpful.
kind regards
Victor

Josh

Good stuff and exactly what I was looking for….Thanks!

Beck

very good keep it up

Peyton

This would have been more helpful if you gave the specs on the original file before encoding (i.e. file size, length of video file, maybe a screenshot for visual quality, like a before and after deal). I don’t know which setting I should use for my source because I can’t compare your results to your beginning product, if that makes any sense.

AbsTechie

Great post man!Really saved all my efforts!

Anonymous

Thanks so much! I learned something new today.

gachzorge

Hey, I’m just curious if audio was a factor in any of this? Or does this compression only compress the video?

Tommy

Thanks for this, you saved me a ton of time! I’m happy I found this, I even bookmarked it. Good work 😀

Anonymous

Hi,

Did you happen to take note of times (even rough will do) it took to run at different RF settings ?

sandeep

Hey ! I have some bluray movies, i just wanted to remove the black bars and want to keep quality intact.. what settings would be best?
If I choose RF – 0, it gives me the file which is bigger than my bluray .. lol
Can somebody suggest please?
I just want the black bars gone. thats all

Adan

Hello Sandeep.

If all you want is to remove the black bars with no size increments in the resulting file, you can try doing some video crop using MKVToolNix.
Simply go to the “Edit Headers” section, and you can set how much “crop” do you want to apply to the file.
That will crop the black bars in the video file without touching the file size.

Make sure you do a copy of the file before trying this option.

Hope this help.

Anonymous

A bluray you can start with RF=22. To get rid of the black bars, just use the default “autocrop” option. In fact, this is a good idea, because not removing the black bars can create artifacts in high motion scenes at the edge of the picture, and also you don’t want those black bars taking up disk space when in fact, they’re just blank black bars. So always crop them off!

Anonymous

You should mention that those “black bars” are in the actual picture frame used in the camera. I understand that removing the bars reduces filesize, but those bars are not “just blank black bars”. They actually contribute to the correct contrast and brightness of the entire picture frame. It just comes down to what quality you are comfortable with for one specific picture (e.g. Action movies are quite different from documentaries so quality settings are not fixed values for all types of film material). I normally use the following settings for (Action movies) Blurays: Anamorphic: Strict, Cropping 0:0:0:0, All filters off, Video RF: 18, x264 preset: Very slow, x264 tune: none, H.264 profile: high, H.264 level: 4.1.

Matth
Matth

Definitely best for everybody to save some time and read the manual. It clarifies some not-so-obvious things, like why RF0, RF10, and RF18 are not going to look any different:

https://trac.handbrake.fr/wiki/ConstantQuality
https://trac.handbrake.fr/wiki/x264VideoSettings

Yadu

Thank you Very much
Extremely Helpful

Anonymous

How about x264 presets? Would they of affected the quality of your results? Say instead of using very slow you used very fast. Would there of been a difference?

needsaname

I think the actual RF numbers depend on the input video dimensions – 4K and VGA are going to require wildly different numbers to 1080p

Is “RF” the same as “–quality” (or -q) in HandbrakeCLI, do you know?

Woody

What framerate setting do you use for higher quality video?

Karl
Karl

Excellent article, saved me hours of testing!

Jeremy

This is exactly what i was looking for, thanks!
Will changing the value of H.264 Profile and H.264 Level have any noticeable difference in the video quality?

Anonymous

If you just leave the profile and level to auto, x264 will pick a level that doesn’t interfere with the quality you picked.

Walter

Thank You for this very helpful experiment

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