2 pass abr to CRF - a few questions

[Carpo]

I have been reading a lot about how crf gives a higher quality of image due to it being a constant rate, although your never going to know the final size of the file, for years i have always used the 2 pass method so i could fit my backups on to

1 - 3 - cdrs
1 - dvdr
1 - dvd9

But now with hard drives and external drives being so large and so cheap, and with tv screens and resolutions getting bigger i can now afford to have larger files with greater quality.

The two questions i have is -

one

Is there a certain crf vaule used that would cover all files/anime i wish to do, or is it dependent on the type of film, a high action movie may require a lower crf value than say a low action film or an anime.

Two (slight ot for here)

I have always kept the ac3/dts of films, should i continue to do this or use a q5 6 chan aac file.

I have done a few tests using the latest x264 and a 1 hour film using crf 16 - 20 apart from the size of the file - 1.5GB i cant really tell the difference in the image quality.

Any advance greatly appreciated

Thanks :)

[Dark Shikari]

One CRF value is generally good enough for everything. The main exception to this rule is vastly different types of content, such as cel animation vs film, where depending on your eyes and your screen, you may need a significantly different CRF for the same visual quality.

[Carpo]

The main types i do are film and anime - things like ghost in the shell mainly for anime, film is a general assortment, main thing i watch them on is a lcd television, i see a lot of people suggesting either 16 or 18, would you say 16 for film and 18 for anime, or should i just do a few tests on some different animes and see what i feel is best for me?

[Dark Shikari]

The main types i do are film and anime - things like ghost in the shell mainly for anime, film is a general assortment, main thing i watch them on is a lcd television, i see a lot of people suggesting either 16 or 18, would you say 16 for film and 18 for anime, or should i just do a few tests on some different animes and see what i feel is best for me?Testing is simple:

1. Start at a CRF value that you're sure will be high enough quality. Let this value be N.
2. Raise N by 1. Do an encode of a test clip.
3. Is the quality still good enough? If so, GOTO 2.
4. If not, drop N by 1 and use this CRF for everything.

[Carpo]

yes thats what i have been doing, guess i will have to do more :) - Thanks Dark Shikari

[Chengbin]

For me, I use CRF X for film material, CRF X+4 for anime (no detail, you can get away with high CRF value), and CRF X-2 for animated movies like WALL-E, Kung Fu Panda, etc (because due to the way x264 works, using CRF X would give a really "undersized" file, where quality suffers)

[Carpo]

what are peoples thoughts on the 2nd question - the audio one, or is it more a fact i am going to have films that are high in GB's, that a few hundred meg, or even a GB in some dts files isn't going to make much of a difference ;)

think i will do a test of 16 on a film clip i have made and 18/20 on the gits anime - see what i think :)

[ronnylov]

You may need a lower CRF when encoding at lower resolution because when enlarged to full screen the encoding artifacts will be more visible compared to a high resolution video viewed on the same display.

[Sharc]

Testing is simple:

1. Start at a CRF value that you're sure will be high enough quality. Let this value be N.
2. Raise N by 1. Do an encode of a test clip.
3. Is the quality still good enough? If so, GOTO 2.
4. If not, drop N by 1 and use this CRF for everything.
I know there is no way for file size predictability with crf, but here some results of a 2 hours clip which are nevertheless a bit surprising to me:

crf -------------- relative file size
19.8 -------------- 100.2%
19.9 -------------- 100.1%
20.0 -------------- 100.0% (reference)
20.1 --------------- 76.3%
20.2 --------------- 76.2%
20.5 --------------- 76.1%

What surprises me is the big step in filesize from crf 20 to 20.1.
I only changed the crf value, all other settings were exactly the same. Is this "step characteristic" typical?

[Carpo]

i went with 14 for most SD content as it looked good to my eyes and on the screens it would be viewed, will do a test with some bluray later, will prob use 16 or 18 on that as the image quality is already high, will do more tests with anime to see what crf i will use for that