x264: --psnr used with psy on

[newsky]

Using these settings here:
--crf 18.0 --level 4.1 --tune film --bluray-compat --open-gop --bframes 3 --ref 4 --deblock -2:-1 --merange 26 --slices 4 --aud --nal-hrd vbr --b-pyramid strict --trellis 2 --no-fast-pskip --no-dct-decimate --keyint 30 --aud --partitions all --subme 9 --me umh --vbv-bufsize 30000 --vbv-maxrate 40000 --weightp 1 --fake-interlaced --pic-struct --colorprim "bt709" --transfer "bt709" --colormatrix "bt709" --sar 1:1
In the log error:
x264 [warning]: --psnr used with psy on: results will be invalid!
x264 [warning]: --tune psnr should be used if attempting to benchmark psnr!
x264 core 115 r1995
Is it dangerous? This is wrong? What to do?

Adobe Encode CS5 has poor performance when --open-gop is enabled
If you do not specify --open-gop whether it will be critical?

[LoRd_MuldeR]

Well, the warning should be quite clear: The PSNR (and also SSIM) values will be wrong/misleading with x264's psychovisual optimizations enabled.

That's because the Psy optimizations implemented in x264 hurt the PSNR/SSIM metrics. And the Psy optimizations are enabled by default (for good reason ^^).

Consequently you should use "--tune psnr" or "--tune ssim", if you want to compute/compare PSNR/SSIM values. You should not use these tunes for regular encodes though!

If you just want to encode the video and don't care about PSNR (or SSIM) measurement, you should remove "--psnr" (or "--ssim") from your command-line altogether.

BTW: Using "--open-gop" gives some extra compression efficiency, especially with very short GOP's (as required for BluRay). But you can safely keep it disabled.

[nixo]

Odd. I don't see any --tune psnr in the command-line.

@newsky: You've got --aud in there twice.

--
Nikolaj

[LoRd_MuldeR]

Odd. I don't see any --tune psnr in the command-line.

Well, that's exactly the problem here. However there is no "--psnr" in the command-line he quoted either :confused:

Still the warning clearly indicates that he was using "--psnr", but without "--tune psnr". So he obviously didn't quote his complete command-line.

Anyway, the solution is to either remove "--psnr" (if PSNR calculation is not required) or to add "--tune psnr" (if the goal is PSNR measurement).

[nixo]

However there is no "--psnr" in the command-line he quoted either.

Right. That's what I meant to say. You'd figure the log came from a different encode.

--
Nikolaj

[TomBombadil]

I am running Debian testing and for some weeks now I see the same messages
x264 [warning]: --psnr used with psy on: results will be invalid!
x264 [warning]: --tune psnr should be used if attempting to benchmark psnr!
As I use x264 (libx264 to be more precise) indirectly via handbrakeCLI I first checked to see whether it is an issue of handbrake or x264 by downgrading to Debian stable.
Issuing the same commands via shell script I got identical logs which were but missing these warning messages.
The maintainer gives the packages specification as libx264-115 (1:0.svn20110617-0.1).

My question is the same as that of the original poster: Anything to worry about?

[Dark Shikari]

It doesn't mean anything except that the PSNR scores won't be of much use.